This could easily be circumvented by having the AI generate an explanation of the chosen portion of code and have the human rewrite it in their own words. It is much easier, imo, to swap clauses and put synonyms in place of other words within existing writing then it is to synthesise new text.

Right. Reviewers still have the advantage of being able to spot AI text because it's often overtly different. I just meant to say that, if you prompt ai "what would a human be proud of having written this code" you'll get an answer. They're not categorically incapable of fabricating an "opinion", they're just trained not to express one by default.