I'm not familiar with Sol LeWitt. I guess whether I'd consider him an artist or not depends, as you said, on how much control he has over the output. For instance, if his instructions were something along the lines of “paint a rhinoceros for me that looks like it might have been done by Picasso and that uses only the colors blue, green, and yellow,” I wouldn't consider him an artist at all, just as I wouldn't consider a person entering that same prompt into a generative AI an artist.

On the other hand, an architect who gives precise specifications for a neo-Gothic cathedral could very well be considered an artist even if he never lays a brick himself :)