...........

Are you serious? Please don't act like the I was supposed to know that he will give actual criticism after his very first comment, to which I assumed is just a ragebait and jokingly called as such.
His very first comment was literally: "Translation doesn’t flow well, grammatical errors, at least better than this other group's MTL. Get a better proofreader." Now, I'm not sure about you, but I don't see any valid criticism there, it was straight up just dismissive and condescending... it could even be said that it was an insult by framing it like we're barely better than the horrid demonic scan's version. He only added actual examples after I reacted by saying it's ragebait, but I acknowledged the examples after he gave them, so acting like I "refused criticism" ignores how the whole thing started.
About your other points:
- who/whom does create a more "formally complete" sentence, but what I meant was that in everyday natural speech, native speakers often drops the relative pronoun, so mine was more conversational. For example: "He's the guy I told you about" or "The girl I saw yesterday looked familiar"
So, no, leaving out the relative pronoun is not "wrong" automatically. I did acknowledge his correction, I just said I prefer mine over a more formally complete sentence.

In case you misunderstand again: I agree that he's right about this one, but several others were still preferences than actual errors, which you conveniently ignored again.
- The "I worked as an official editor": Please look at the order of the messages. That was after my ragebait comment, and his immediate reaction was that "Learn to take criticisms. I worked as an official editor and typesetter for over a year." (like I was supposed to know that)
Once again, I'm not sure about you, but to me it seemed like he wasn't just simply adding context for his claim, but was using that as a way to position himself above me, as if to say "I’m qualified, you aren’t, so accept what I say". But... sure, let's give him the benefit of the doubt, maybe he did just frame it bad and didn't mean any harm, and if that's the case, then I apologize.
- That "waste of time" comment wasn’t about his criticism, it was about the whole situation. He felt the need to take me down a peg just because I dared to be a little proud of the work, and not sure if you noticed, but I removed my comment in case people like him (or you) tried to escalate it even further.
All in all, you can also do better than this.

I'll stop commenting, hope you guys stay happy in whatever going on with your lives.
Edit: Bro literally added a little note to talk shit before I could type my comment 😭what in the passive-aggressive. Anyway, you don’t get to call someone "egocentric" just because they don’t immediately grovel the moment a stranger starts with how "Translation doesn’t flow well, grammatical errors, at least better than this other group's MTL. Get a better proofreader."
NO ONE would treat that as a good faith criticism on the very first read. You are literally rewriting the narrative so it frames me as an egocentric prick who dismisses any criticism, even though I just responded the way anyone would to such a condescending message. Honestly, this says a lot more about you than me.