The irregularities you are complaining about are irregular only if you think at the letter level. For someone who is used to thinking at the syllable level (Japanese, Spanish, Italians) it’s a regular system. And no, picking consonants from “basically any major West European language” would not have made it understandable without asking to speakers of other Western European languages. Because my “which j, which ch, which z” refers precisely to differences in which phonemes those letters represent in different languages that use Latin alphabets.
Again, we’re talking about the use of a romanization in a context where the primary consumer is Westerners, in a writing system that is designed around consonants and vowels rather than syllables.
And while (for instance), the use of Spanish consonants would not be immediately obvious to a English speaker, they could adapt pretty readily once they’re told that the consonants are pronounced like they are in Spanish. Or Italian, or German, or whatever. Just be consistent. I mean, you could just as easily develop a romanization where “k” sounds (か group if you want to get nitpicky) are written with a “b”, “g” sounds (が group) are written with a “c”, etc, and while Japanese speakers wouldn’t notice a difference we can agree that would be a rather ridiculous thing to use to communicate with Westerners, yes?
Here’s a situation in which I believe that we are going overboard with uniformization. If the Japanese government is making signage, then obviously it has to choose a standard system.
However, otherwise, there’s no reason why a text in English, a text in Spanish, or a text in German, for example, all have to use the same transliteration system for Asian words.
Each language should transliterate the words in whatever way makes the best sense for the targeted readers.
A Thai who travels abroad will have one (1) passport with his/her name written with Roman letters. Should he instead have separate passports for travel to separate countries?
If a Thai has pen-pals or Facebook friends from six different countries, should he spell his/her name six different ways?
Mail to Thailand from abroad often has addresses written in the Roman alphabet. Should the post office, and mail recipients, cope with several different ways to render names with the Roman alphabet?
Many street signs in Thailand have names shown both in Thai and with Roman characters. Instead of two renderings, should the signs use smaller print and have room for seven renderings?
Someone from country A emigrates to country B and then wants to move to country C. This can lead to bureaucratic snafu if B and C transliterate the language A name differently. Should that immigrant just be “out of luck”?
Spanish spelling is syllabic; it’s not “one letter, one phoneme”. There are letters which get different pronunciations as part of a consonantic digraph, others which change depending on their position within the word, and yet others that change depending on which vowel or vowels come right after. There’s also a couple of weirdos which change depending on which language we adopted that word from, but thankfully they’re not very common. Conversely, certain consonantic phonemes will get different spellings depending on their accompanying vowel or their position within the word. So, to pronounce the consonants “like in Spanish”, you need to begin by learning to think of pronunciation in terms of syllables. Just like in that Japanese system.
That’s funny, lingyi. Whenever I speak Chinese to native Mandarin speakers, they comment on my Beijing accent. That’s where I first studied Chinese. I don’t mind it, but it must sound odd to Chinese, like a Chinese speaking English with a Bostonian accent or something. I can’t help it, though. When I throw off casual phrases it just comes out that way.
“Do you speak Chinese?” “Yi dian(r).”
FWIW, I know a guy who works outside of Japan, and he spells his name (professionally; I don’t know what’s in his passport) according to the “official” system, so it’s not just a theoretical possibility. Beats me if “basically all Westerners” pronounce it wrong; people who work with him know what his name is.
BTW I also know a couple of people, from Taiwan and Korea, who at some point seemed to pick up an “American” name/alias. Also one from Thailand, now that I think of it. What’s up with that? At least one of them was vaguely annoyed that people would consistently butcher the romanized spelling. [But OTOH I know people whose names are at least as unpronounceable who have never even considered altering their names.] But what do you do when you next travel to Germany? Or Russia?
I use different spellings for my firstname depending on which one will the locals pronounce more similarly to how I do. Aside from Spanish and French versions, I use two different English ones because some people will pronounce the /a/ correctly if I start Mari… and some will do it if I begin Mary… While this turns out to be something Hispanic people in general tend to do, in my own case it stems from the first time I was out of the country: both my host-mother and my teachers did some really nasty things to their own throats as well as to my poor name, so the alternate spellings are actually a matter of public health.
I had a coworker called Gorka (the Basque version of George). In Spain, anybody trying to call him Jorge would have been skewered; in Scotland, when the locals looked at his name and went “uh…” he automatically said “George, it’s just George”. Another coworker was a David: same spelling, different pronunciations depending on what language we were speaking. It’s just a change of register, like using more or less formal language depending on whether you’re having a coffee break or a videoconference.
LOL!
I have only a very rudimentary understanding of Mandarin and Cantonese (from decades of watching Asian movies), but when I watch a movie where people are speaking with a Beijing accent, it reminds of someone speaking like a Ha-vard or Yale graduate! 
Edit: I’ve mentioned this before, but since I learned Chinese celebrity names primarily from Hong Kong movies and award shows, I’ve been told I speak with a Hong Kong accent! Especially when I use the Mandarin names for Mainland and Taiwan celebrities.
It’s popular in Mainland China and Hong Kong also.
What’s really great is when their English name really close to their Chinese name. A prime example is Hong Kong singer Joey Yung (容祖兒). Her Cantonese name is really close to Joey (Jyo yi).
Then there’s people who go the opposite way like director Fruit Chan Gor. I can’t find it now, but I swear I read a story about how he got his name.
Finally there’s disasters like Aman Chow (Chow Yun Fat) and Gianna Jun (Jun Ji hyun / 전지현) of My Sassy Girl who tried to break into the American market with Blood - The Last Vampire. Thankfully, both have reverted to using their proper names (or stage name for Wang Ji Hyun).
What’s wrong with Gianna? Is it because it’s originally an Italian nickname? Most of the names that are common in the Western world originated in a different language than the ones currently using them. All those Biblical names, for example.
It’s terrible because Ji Hyun is one of the biggest stars in Korea and should be recognized for who she is, by her Korean name. From what I’ve read, Gianna was chosen because it’s somewhat phonetically close to her given name which is difficult for non-Koreans to pronounce correctly, especially her surname.
I didn’t know that the origin of Gianna and it makes no difference to me that’s it’s Italian. I’m sure there’s some famous actress of any national origin with that name, given or stage and I’m fine with that What I take take offense at is Hollywood (with admittedly Ji Hyun’s acceptance) trying to repackage someone of her status for the Western market with an unnecessary, IMO Western name.
I’m especially aware of using celebrities proper names (i.e. based on their country of origin) because of the number times I’ve been corrected, often sternly when I used the Cantonese names for Taiwanese actresses instead of their proper Taiwanese names.
Thankfully and IMO, rightfully (I tried but couldn’t watch my beloved Ji Hyun in such a terrible film), Blood - The Last Vampire flopped and Ji Hyun returned to Korea, with her appearances in movies and TV getting rave reviews.
Oh, OK. Right, it’s the whole “no you can’t call yourself Schwarzehow do you pronounce this anyway” thing. Agreed with that.
Some Korean Christians (a plurality of ROK’ans, a majority of the Korean diaspora in the US) go by their Christian name. As in literally their baptism name, as opposed to old Western convention where “Christian name” meant “given name”. It’s true, others go with a Western name similar in sound to their Korean given name. I don’t see a problem either way. I happen to be familiar with the Korean language but that’s not usual outside Korea, and people may want to remove a barrier to addressing them, it’s just practical not some act of self negation. Though I don’t think anyone else should require it.
Some people I know in Korea address me with a one syllable mononym that’s an abbreviation of my surname which is harder for them to pronounce correctly as a whole. Or, they’ll call me by the Korean Catholic (ie ‘Latinized’) version of my given name (like if my name were Anthony it would be Antonio, 안토니오, and so forth) not my actual given name. Those versions were adopted originally I believe because Latin/Romance language sounding names tend to easier to transliterate and pronounce accurately in Korean than Anglo-Saxon/Germanic sounding names. It’s not only in West that different name versions are adopted or used because easier to write or say.
In answer to the OP’s original and follow up post, the bottom line is that at least for most Asian languages*, all forms of romanization do a poor at best, job. There are way too many nuances of pronunciation that can’t possibly be captured by the English alphabet. Resign yourself to having to explain the proper pronunciation of Thai names and words.
That’s what baptismal name means in Spanish-speaking and French-speaking countries. I know, I know, we’re not Western 
*Missed the edit window on my previous post.
Romanized Japanese and Hawaiian (which originally has no written form) is actually really good once you know the phonetics of the languages.
An interesting thing is happening in Kpop in regards to romanization of Korean and Chinese names. Here’s a couple of examples, the Taiwanese member of Twice (which also has three Japanese members), Tzuyu (子瑜is) almost always referred to by that name (which is Taiwanese) when written. However, verbally she’s called by her Korean name, Jjeuwi (쯔위), which almost every non-native Korean speaker mispronounces as “Chewy”. I’m sure there are a good number of people who think Tzuyu is the proper romanization of Jjeuwi!
There’s a similar situation with former Pristin (the group just disbanded) member, Jieqiong (洁琼) who is from mainland China. She’s better known in Korea by her Korean name Kyul Kyung (결경) and is usually referred to by that name in the press, though I’ve seen articles where they use Jieqiong along with the other members names, who are all Korean.
Those are actually two different treatments of a foreign name in Korean which might be illustrative. A Korean with the given name 子瑜 would be 자유 (Ja-yu). 쯔위 is not a ‘Korean name’ any more than the hangul rendering of my full Anglo-Saxon given name is my ‘Korean name’ (though I guess some people might term it that way). Both are just foreign word/names written in hangul.
In contrast, 결공 (Gyeol-gong, in current official ROK romanization, not quibbling with your transliteration, none are exact) is the Korean pronunciation of 潔瓊 (again not quibbling but that’s how you’d write those characters in Korean, in traditional form) and different from the Mandarin pronunciation. That, I would say, is more like a foreign person’s ‘Korean name’.
This situation used to generally be treated the second way. Chinese character foreign place and person’s names used to generally be written in hangul the same as those characters would be in a Korean place or person’s name. In recent decades it’s become much more common to go with the first method, and write foreign Chinese character place and people’s names in hangul according to the foreign pronunciation of the characters. But if speak Korean but not Chinese or Japanese, know Chinese characters well (which a lot of younger Koreans don’t, but anyway) and see a place or person’s name written in Chinese characters, at first you only know the Korean pronunciation, IOW the second method is more natural. The first tends nowadays to be viewed as more polite toward foreigners, and perhaps paradoxically ‘more Korean’ in emphasizing the hangul rendering of a name as its essence, rather than the underlying Chinese characters as its essence.