This actually hits on a couple of the reasons why I get skeptical when I hear that underhand free throws are better.
I don't deny the science or the fact that some individuals don't do it because they think it looks dumb. But I'm inclined to think that over time the best, most effective technique will win out. Like you said, there's nothing inherently "cool" about a traditional jump shot, thats just what works. I think chances are Barry was so talented that he would've been a great shooter regardless of technique.
And if you just objectively look at the top 50 FT shooters of all time, you'd see that 49/50, including the top 6, all shoot a traditional looking shot, so that's clearly a proven and repeatable technique.
Now, to play devils advocate to myself, it's also possible that the most successful technique is just the one that is taught the most from a young age. If there were more coaches teaching the underhand method in grade school, maybe we'd see more of it in college and the pros?
Anyway, I don't mean to sound like I have some kind of vendetta against the underhand shot. I think players should do what works for them. I had a coach in Jr. High who taught us to take one big step forward with our right foot, one big step back with our left foot, lean forward with our right elbow over our right toes and shotput the ball up there because that was his technique he used in college and once made like 19/19 in a game. It worked for some of us but I think most of us reverted back to the traditional set up.