Well L. Ron and John Smith are automatically discounted as prophets because Baha’is believe Bahaullah was the manifestation of God for this era, and that there won’t be another one for at least (let me google, I can never remember)…1000 years after 1863 which is when Bahaullah declared his revelation. If you graph the accepted Baha’i manifestations, they tend to come between 500-1000 years apart except for the Baab and Bahaullah who lived at the same time but never met in person.
But I think you are really asking, what makes the accepted manifestations/prophets different from the discounted ones before Bahaullah? If so, I will be honest and say I am not sure why the orthodox prophets were decided the way they are…though like most things I am sure there is a scripture with an explanation, I am just ignorant of the passage (the canonical Baha’i writings include MANY volumes!).
Interesting side note, but the accepted manifestations, Krishna, Zoroaster, Buddha, Mohammed, etc, are not ALL of the manifestations, just the ones we know about, it is implied in certain writings that there were Native American manifestations of God that we don’t know about who were lost in oral traditions etc.
I acknowledge my tremendous ignorance about the Baha’i Faith too, and I am one! I have attended classes which are very similar to sunday school classes you might be familiar with (but Baha’is meet at each other’s homes to encourage community, we don’t really have churches in the same way), but there is a TON to learn, but living a Baha’i lifestyle is fairly simple IMO there aren’t too many burdensome rules. Lack of drinking and marijuana is definitely not easy with my group of friends and the fact that I was a convert as an adult.
Anyway, what makes Bahaullah “legitimate” to me, and one of the biggest reasons I became a Baha’i, is because I had a feeling my whole life that the Bible was more appropriate for people 2000 years ago, than modern people. Civilization has come a long way since then, slavery is condoned in the Bible. I have never seen another religion that so embraces science and literally says, if a scientific discovery discounts a religious claim, then that religion is wrong. Look at Climate Change denialists and young earth creationists… they are denying simple reality because it contradicts their book, hurting their faith in the process.
So ideologically and politically I agree with Baha’i beliefs more than any other religion, it just fits me, but beyond that when I read Bahaullah’s words they echo in my heart and soul in a way that I never experienced at all growing up Christian and reading the Bible. I always knew I was religious but I had way too many problems with Christianity, and by chance one day I saw a glimpse of a Baha’i membership card in a customer’s wallet and I asked him about it, and here I am.