Good god! Does that mean the rest of the 1968 Beatles bio by Hunter Davies isn’t 100% on the level? 
I have played guitar for going on 40 years, though not in a band for a long time. I have actually thought about this one. My bands played basic toe-tapping rock. Picture classic rock playlists: Beatles, Stones, etc.
Very little finger-picking in our repertoire. I am a terrible finger picker–I am just now working on it, and after all these years it’s not intuitive to me. Typically, if there was a song I learned to finger pick (e.g., “Dear Prudence”), I did it with two fingers, thumb and pointer, sort of half-assing it. I could hit the notes if I practiced it, but I’m sure it wasn’t an efficient pattern.
Four-fingered picking, following standard patterns? Not something we ever did much of–we didn’t do any folk, or Paul Simon, or whatever. That’s not what we wanted to play. There’s lots of great rock guitar players (not that I’m saying I’m one) who can’t finger pick and hate to do so (e.g., Eddie Van Halen). The stuff we did play, ISTM, was much more reliant on the left hand for advanced playing. Both hands are important, obviously. But the hottest guitar players became so (in our genre) with their left hand, through hammer-and-pull-off techniques, through trills. Tapping the fretboard with your right-hand fingers augments these techniques, but for me that part feels easy.
Now, it may be that the right hand parts in the genres I play seem easy BECAUSE I’m using the right hand–i.e., I’m confusing cause and effect. But I don’t think so. I’ve argued that with my bass player. If you’re Paul Simon, you want to play standard. If you’re, say, Billy Gibbons (or the rest of the guys I played with), you’d be better playing lefty. My two cents (worth exactly that).
Wow, Stratocaster, my mileage does indeed vary. I may not be Mr. Fingerpicking but I look at my RH technique as very complex. I do so much muting and picking dynamics - varying my attack, pinching harmonics, locking my palm down to mute the strings for hard rock chunking rhythms. I think the balance in dexterity between hands tips towards my picking/strumming hand. And with my recent forays into hybrid stuff where I flatpick but also throw my middle and ring finger into the mix, even more so…
Yeah, again, I could be confusing cause and effect–maybe the right hand part seems easier because I’m using my right hand. And I did think about the role the right hand plays–muting strings, etc. My unprovable speculation, though, is that most guitarists in the genres I play would have been better if they learned southpaw, that of the two hands, the one that makes a hot guitarist hot to a greater degree is the left hand (bending the string, hammer and pull off, trills, etc.).
You and I both know, of course, that good guitarists have to master both. It just seems to me that non-finger-pickers are relying on a convention that was not designed for their genres. All I need to prove this is a time machine, so I can go back and learn to play left-handed, and see how it turns out. 
I’ve been playing around forty years. I play left-handed, and I reverse the strings (so my thumb is on the thick string side, and the thin strings are closer to the floor).
Even though I’m right-handed at pretty much everything else, I don’t believe that playing left-handed has hampered my playing at all. (This bolsters the case that a person who writes/throws/etc left-handed should consider playing guitar right-handed. It also raises the questionof why I learned to play this way - the only answer I have is, I didn’t know any better). Playing the guitar is a skill where the two hands work together (like batting) as opposed to one hand working in isolation (like throwing). While very few can throw both righty and lefty, lots of people have learned to bat both ways.
One major drawback to playing the way I do is that I can’t play a standard right-handed guitar, which is about 99+% of them. So if I expect to, say, sit in with a band, I have to keep my guitar nearby. (An associated benefit is that it dissuades drunks in bars from asking to play my guitar.)
A major downside to playing left-handed without reversing the strings: you’re at a disadvantage for fingerpicking. Much fingerpicking uses the thumb like a piano player uses their left hand (to play the bass parts) - the fingers are used like a piano player’s right hand, to play the melody and chords. With your thumb on the thin strings, you’re very limited in playing much fingerpicked material. One of the few fingerpickers who played lefty without reversing the strings was Libba Cotten, and while she was a great player, her technique limited her to her own creations.
I’ve had people respond to this point by saying they don’t want to fingerpick, they just want to flatpick. I would simply point out that you may change your mind down the road. I started out just using a flatpick, and didn’t get interested in fingerpicking for decades. So I’m very glad I reversed the strings when I started. Stratocaster’s next-to-most-recent post points this phenomenon out: you end up essentially limited to a two-finger technique.
That matters. Just sayin’ as a GAS sufferer (Guitar Acquisition Syndrome) that having the spectrum of candidates stripped down that much would be yucky.
I suspect that most folks could swap the roles their hands play. Given the stuff I play, I love that my dominant hand is my strum / pick / mute hand. The fact that most guitars are righty is a real advantage.
How is that any different from the usual arrangement?
My sister majored in music in college, so of course she’s now an expert. But her first attempts at playing guitar when she was 13 bemused me, because she called the bass strings the “high strings” and the treble strings the “low strings.” I told her no, she’d gotten it backwards. She didn’t follow what I meant. Turns out she was naming the strings by their position in physical space instead of music-staff space (even though she already played piano and could read music staves). Logical enough, in its way.
Some people might think “usual” means leaving the guitar strung right-handed and flipping it over; others might think that reversing the strings is usual. I spelled it out to avoid this confusion. And I spelled it out so explicitly, using hard-to-misunderstand descriptions, because I’ve often seen people make the very mistake your sister did, mistaking “low” to refer to position instead of pitch.
Lefties look at guitar acquisition differently, through sad eyes.
For years, I loved the sound and look of resophonic tricone guitars, which were used on lots of early blues and Hawaiian music records in the 1920s and 1930s. But National didn’t make lefty tricones until 2006. I was in Iraq when I learned they were taking custom orders for lefty tricones, and I stood in line at a rec center phone to order one (I got the fourth one they made). I played it for a year or so before realizing that it didn’t suit my playing style and voice as well as another National that I’d bought earlier. If I were a righty, I could have walked into a store and found that out for free in a day. (I still play the tricone sometimes, for variety, but I doubt I would have bought it knowing what I do now).
One of the strongest arguments that playing righty is no hindrance to left-handed people: **many accomplished guitarists are left-handed, but play right-handed. **Two off the top of my head are Glen Campbell (not a hall of famer, but a professional, who in addition to accompanying his singing, worked as a studio player) and George Van Eps, a true immortal by any standards. (I recall those two from an article about lefties in Guitar Player ca. 1980. Curiously, Van Eps responded with an letter complaining that the article might confuse readers interested in buying his instructional materials if they thought they were designed for lefty play. “I play the right way”, he angrily clarified, “picking with the right hand!”)
Over the decades, having small hands has been more of a hindrance to my playing than any handedness issues.
Glen Campbell is an excellent player. And yeah, GVE is a master of the “lap piano” as he called his approach - I think he played 7-string, influencing Bucky Pizzarelli…
And yes, maintaining access to the world of right-hand guitars is a HUGE advantage. You discuss targeting a specific model; from another approach, I have discovered so many guitars serendipitously because I try to play everything in the shops I visit and keep an open ear.
And there is one other advantage to playing lefty (and reversing the strings): it helps with teaching, because putting my guitar neck so it’s facing a right-handed student’s guitar creates essentially a mirror image. Much easier for the student to follow what I’m doing than if I were playing right-handed.
That helped a lot when my Uncle was teaching me knots. Although I learned them all backwards. Plus side other people have a hard time untieing my knots.
Actually not a strong argument. First of all, who knows how much of a hindrance it was to them? Just because they can do it doesn’t mean there was no hindrance in getting there. Secondly, what may be a minor (or non-existent) annoyance to one lefty could be a major impediment to another. One can make a reasonable (not strong) argument that playing righty is not a complete hindrance (not no hindrance) to some left-handed people (not left-handed people as a whole, we’re not that monolithic). It’s likely that most lefties who play righty do so not because there was no hindrance in playing righty for them, but because they encountered a huge hindrance in even finding a lefty guitar.
Back when I was teaching full-time, I always offered to let any left-handed student borrow one of my guitars, to see if it suited them better. Only one ended up buying herself a lefty guitar, which were readily available through the store by custom order. Out of the hundreds of students I’ve taught, I had one other student who played lefty (he had bought the guitar before he came to me for lessons, so I wasn’t going to make him get rid of it).
There are of course differences among individuals, so I can’t categorically refute your points. But my experience seems to differ from yours.