fortunate son is not a very good song. It's not terrible, but it's bland and repetitive. It's not my favorite creedence clearwater revival song even if it's their most popular. Suzie Q. is probably my favorite.
(Warning: words words words about a different classic rock group)
To add onto that, I don't think Syd Barrett's schizophrenia was as bad as they make it out to be; I think they exploited him, and they overplayed his disorder to create a modern Greek tragedy, a tale for wives to tell, and a marketable tale that would solidify Pink Floyd's legacy.
He seemed overall coherent even during the points when he seemed most out of it. (i.e., the "Have You Got It Yet?" tale.)
Then you have the fact that music wasn't his main hobby or interest; he dabbled in other forms of art like painting (which was something he had been doing since the early '60s) as well as carpentry.
So he was still active as an artist even when he gave up the guitar after 1972.
Finally, he was never formally diagnosed with anything. He could've just had a psychotic episode and moved on with his life, out of the limelight. What's unfortunate, though, is that he's not here to confirm nor deny any of the rumours, as he's been dead for 19 years. So it's not like he can defend himself against the allegations, which is fucked up.
Another thing that could've fuelled those rumours was that back then they used to think you 'went mad' if you did acid. Which isn't entirely true.