I saw your question about Endgame, so I wanted to share the reasons I don't like it and the reasons I've heard other people don't like it. My gripes are more structural than direct because I actually stopped watching the MCU right before Endgame. I didn't like how the ensemble movies were, much as these big events are complained about doing in comics, hurting the standalone stories. Be it how Infinity War reversed a lot of Thor's character progression from Ragnarok and Endgame apparently spent most of his screentime making fat jokes and mocking him being depressed about the massive losses he's suffered, or how the Endgame-teasing stinger at the end of Antman and the Wasp immediately tanks the tone of the entire movie. Speaking of Infinity War, it feels like an incomplete movie that screeches to a halt and then isn't actually picked back up by Endgame.
I also personally don't like the whole three years blip people gone thing. I don't like that Tony Stark gets to go out framed as a "martyr" after his multi-movie arc of making things Worse while the reason the Avengers aren't seeking to undo the Snap entirely is so he can keep his relationship and daughter and not make a personal sacrifice when that's not where his character has been going.
As for what I've heard from others who've actually watched the movie, yes, Steve and Bucky's situation is a gripe but it's less "Stucky not canon! D: " and more "direction so determined to Keep Things Hetero they swung around into character assassination". People don't like that he ignores his best friend and people don't like him going against his comic-book-established character to return to the past (altering Peggy's life and years and accomplishments spent without him, too!) instead of moving forward. People don't like how Natasha was sacrificed, either, I'm pretty certain. Or the Thor Fat Jokes.
I also feel they've done every ensemble plot except the original Avengers and *maybe* Ultron *too early* and that just using them because they're well-known whether or not they were good or well-received in comics is not a good strategy. Civil War split the fandom for very little reward and it's hard to get invested in the stakes of anything after the shark-jump that is Thanos.
A lot of this is foggy memory, hearsay, and personal opinion about a cinematic universe I've stopped engaging with for the most part, but I hope it's been of some help in answering your question regardless.
I appreciate you sharing your personal feelings on the matter. I understand your feelings towards the team up films but I can't say I share them. I would say, maybe you should go back and watch through the franchise to break down and build up your thesis on it, I would be delighted to see what any research turns up.

















