In Bob Ross's defense, not saying anything about his art, he lived in Alaska for a long time and observed a lot of nature. He also enjoyed getting out into nature. He at least had a notion of what nature looked like.
In defense of both Ross and Alexander, even Rembrandt used wet on wet on occasion. Their big contribution was getting people thinking about creativity and expression. As Ross was big on saying, it's your world, make it what you want. Isn't showing OUR OWN world a big part of our photography?
I agree about folks using tricks to make their work look the same, though. It bothers me that many of the local "pro" photographers copy each other and there is no real variety or expression. It's to the point that people are selling Photoshop actions to make your photos look like they were taken by them, not you.