I find that a lot of the things that frustrate me about BL/GL comics are things that frustrate me about written romances in general, even straight ones: stalking and cruel behavior seen as romantic, one person wearing the other down into "giving them a chance" at a relationship, and unrealistic sex to name a few. Characters who are lauded as a good/positive couple but that lie to or manipulate one another for their own gains without consequences. Pretty much anything that is presented to be a normal/healthy relationship (or the main/good relationship of the story) but that are creepy or abusive gets my hackles up. This is way different than relationships that are supposed to be abnormal/dark/complicated- which I absolutely love- but too often I see stories that are romance and total fluff that have really... off things in them and the author seems not to realize. Context is key in a lot of those situations.
But I also don't see this as an issue of BL/GL, but sexist culture in general. I see these a lot more in straight romance and straight romcoms than I do specifically in BL/GL: if anything they're just following in the steps set for them by straight fiction, but held to an unfair higher standard. I think all of it should be improved, but it's not LGBT+ content's fault alone.
If anything, the one thing in GL that drives me personally bonkers is how wlw is generally seen as nothing but fluff, without much adult intimacy ever shown. The whole "men have sex: women cuddle" thing. But again, these are aping from straight sexist stereotypes about women, so not really surprised.
I don't know if the assertion that most BL/GL is written for/by straight women is really a thing, especially here in the land of webcomics. For my credentials, I'm a bi lady myself.