The main problem is finding Artist images to start off with, rather than choosing between them. I don’t know how Roon resolves a choice of Artist images. I suspect it chooses the highest resolution.
There is good discussion of Artist image improvement in this thread.
I had a good discussion with Mike, Noris et.al in this thread, nothing resolved. However, as I pointed out earlier Plex along with others have working solutions to avoid a box with nothing in it.