What Dilbert is saying is that salaries paid in his company are really ridiculous, implying that the artist does not make even a minimum with his art, which in itself means that he's not selling at all. The artist says that he doesn't need to sell, but isn't Wally right when disputing the worth of an art career that is not being welcome by nobody else? Bottomline: you might do great art, but the title of artist depends of acknowledgment by others.
A pity to get all sensible about a comic strip, I know, but I don't think it has been established that his art is terrible at this point. Dilbert assumes it is without having seen it and Wally then makes a statement that is obviously not true without having seen it.