Who’s the definitive authority of “level of art”? There isn’t one because, by definition, art is subjective. Just because you see it as “lower effort” or whatever doesn’t mean it can’t be a high “level of art”. Piet Mondrian drew lines and colored in some of the boxes. Seems pretty amateurish to the “uneducated eye”, but they’re still held in high regard.

The botched Jesus painting restoration effort. Everyeone is in agreement of the result not being art. https://en.wikipedia.org/wiki/Ecce_Homo_(Mart%C3%ADnez_and_G...

I'm not saying Ross' painting is as bad as this extreme example, but to even a casual appreciator of world class art, Ross' paintings are of very amateurish quality. The stuff you'd see hung in a motel breakfast corner for example.

What are some example reasons why Ross paintings are of amateurish quality?

I've seen plenty of motel paintings, watched plenty of Bob Ross episodes, but the comparison doesn't seem fair. Motel paintings are often printed - you can tell by the CMYK dots if you come close enough. Ross at least seems to use actual oil paint on canvas supported by real solvents which seems a lot higher quality than the usual school process using acrylics or temperas. (Although granted using liquid white seems a bit dodgy).

So what is Ross missing. Not enough detail? Does not take enough time to paint a painting? Not enough paint on the canvas? Not photorealistic enough? Too photorealistic?

Ross' attempt at realism fails. The paintings are neither realistic, nor an appealing stylistic take on realism.

I would apply the uncanny valley dynamic to his landscape paintings. https://en.wikipedia.org/wiki/Uncanny_valley