As far as I've ever heard, "le code" used in a codebase is uncountable, like "le café" you'd put in a cup, so we would still say "meilleur que tout le code que j'ai vu en 20 ans" and not "meilleur que tous les codes que j'ai vus en 20 ans".

There is a countable "code" (just like "un café" is either a place, or a cup of coffee, or a type of coffee), and "un code" would be the one used as a password or secret, as in "j'ai utilisé tous les codes de récupération et perdu mon accès Gmail" (I used all the recovery codes and lost Gmail access).

Quite sure they're not criticizing your grammar, but your substance.

I guess you can guide it to write in any style.

But what set me off is an universal qualifier: there was no code seen by you that is of equal quality or better that what LLMs generate.

I got curious and had to fire up the ol LLM to find out what the story is about the words that aren't pluralized - TIL about countable and uncountable nouns. I wonder if the guy giving you trouble about your English speaks French.