I guess I'm mostly just confused as to what the alternative solution here is, if Dirk acting this way is inherently problematic. Is it an issue of execution, or are these tropes just completely off limits to portrayals of gay men because of the ability to be read as bad-faith stereotypes?

I totally accept that Dirk being a) gay and b) manipulative and struggling with both of these aspects is core to his character. I'm also going to state my biases upfront: I echo the sentiments that Dirk in the Epilogues doesn't come out of nowhere: Dirk struggles with being manipulative throughout all of Act 6, and his arc in HS proper ends fairly positively with him becoming more aware and striving to Not Be Like That in the future; the Epilogues just present an outcome in which he doesn't live up to that and takes his worst tendencies to the absolute limits.

So is it being a "gay manipulator" that's the issue? Or is it the specific instances and interactions? Like, I understand the idea that Dirk manipulating Dave and Karkat plays into the homophobic stereotype of gay men grooming young men into becoming gay. But there's other things going on there like Dave's repressed bisexuality, Karkat's emotional detachment, and on a meta level with Dirk as an author insert, the commentary on the authorial and fandom impulse to aggressively ship characters. If you ignore ALL of that, then yes, what's left is homophobia. Personally, I think the other things going on here are way more prominent than what is a frankly ridiculous stereotype of gay men. It isn't that I don't think the presence of that stereotype in society is harmful or a problem. It's just for me, centering the stereotype above everything else gives it more power than it deserves and is a limited and reductive way to look at the story.

Or with Rose, yes he is manipulating and "grooming" her. But the stereotype is gay men grooming other men into sex and that's not at all what is going on here? The relationship here is more akin to father/daughter with Dirk trying to get Rose to be his accomplice or subservient to him and break up with her girlfriend he doesn't like (and also the subtext is Rose is also using him but I can put that aside for now).

But like, Dirk is also VERY forcefully manipulating John the entire time. Is that one ok because he's not family? IDK!

And I don't mean to be rude or anything but I find it weird to keep going back to not trusting Andrew Hussie's writing when they just outlined the Epilogues and the bulk of the writing was done by a bunch of queer women who are bringing their perspectives to characters like Rose too? But then on that same note, that means no gay men worked on the Epilogues and maybe that's another problem, lol. Those perspectives probably could improved some of the writing, even if I don't really have an issue with most of the broad strokes.