I think a big reason many artists end up being "good" is because they can create very highly technical works of art and choose not to.

"Why would they draw that?" gets you a lot further in the art world than, "That is a very high quality work of art." IMO for good reason (you are free to disagree obviously).

Hard to say without knowing what was fundamental and textbook throughout the years. I imagine nearly all successful pre-renaissance western artists and most successful pre-photography artists were more or less by the book, but even then, they probably changed things incrementally.

Without outside restrictions, any creative pursuit almost requires deviating from the norm though, even coding. Think of it like this, are you still using only the techniques you learned in college and nothing more? Do you not talk shop with your coworkers and try to think of new ways to do things?

Frederick Hart, Thomas Kinkade, Norman Rockwell. None too well respected, I suppose.

The problem is that there are thousands (or more) young people with all the technical ability of Michelangelo, and so they absolutely need something else to distinguish them. Thus many artists go through their "Michelangelo phase" to get to their "weird scribbly splotchy phase" which is the real lottery ticket.

Perhaps more importantly, the critics needs something to say about art, or they won't say anything. See "The Painted Word" by Tom Wolfe

It sounds like you want an artist who paints in the style of Rembrandt today? Why would a genius deny themselves the license to be original?

Are you talking painting/sketching specifically? I'd suggest Ansel Adams as somewhat consistent. What about Andy Warhol? I don't recall any of his work that went drastically different, but admittedly not an art student

Wyeth (both), Homer, Bouguereau, Sargent, Cox... there's a few.

There are many artists that specialize in styles like photorealism and make a living… but novelty is what gets you to the top