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).
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.
I speak Russian and some English, but the question was about universal quantification: author declares that LLMs generate code of better quality than "any codes" he seen in his career.
I'm native French and nobody would consider code countable. "codes" makes no sense. We'd talk about "lines of code" as a countable in French just like in English.
Codes is a proper grammatical word in English, but we don’t use it in reference to general computer programming.
You can for example have two different organizations with different codes of conduct.
There is though nothing technically wrong with seeing each line of code as an complete individual code and referring to then multiple of them as codes.
And in my French brain, code or codebase is countable and not uncountable.