Surely they can train AI on the signal to change as few lines as possible. Indeed, this is something I'd want to have control over when making requests. In a traditional UI, I'd imagine some kind of slider between "fewest lines" and "be bold".

I'm actually hopeful that the recursive code training will improve quality over time. I'm definitely producing higher quality code, tests, and docs. It does take attention and oversight, iteration and refinement, one cannot just let these things loose on a code base and expect good things to happen. You have to leverage them to make the good things happen.