Bob Ross was famous for teaching the wet on wet technique in an easy to understand format. He brought the ability to paint to thousands of people without having to go to art schools and such. ANYONE could do it and that is what made it popular.
Was he a good artist, most likely. He didn't show it on the shows because that isn't what he was paid for. I'm sure he did go to all those schools and learned all about colors, contrasts, highlights, shadows, spacial properties and everything else they stuff in an art students head.
INK is a pretty good artist as well. He must be to make a living at it. All it takes is practice, and lots of it.
Belial is a dick and was most likely born that way.