The 5 biggest issues with Phase 4 are:
1. The stakes seem considerably lower after Endgame which makes the movie/TV storylines of Phase 4 seem less compelling for the general audience. No supervillain except maybe Doom can match Thanos in terms of being a menacing and compelling supervillain that can convince people to watch all the movies and shows to see what's truly at stake for the heroes in Phase 4.
2. The newer heroes and actors are no where near as marketable as the OG's. I enjoyed Shang-Chi as a decent mythical martial arts movie but Shang-Chi himself is not compelling and there's no real fandom surrounding him. Even actual Asians don't f*ck with the dude lol. And the Eternals suffer from that same problem but worse. That's the main reason why Marvel is still banking on nostalgia bait and the OG's like Spiderman, Strange, and Thor to keep the general public's interest in the MCU. And having Captain America, Iron Man, and Black Panther out the picture makes the dilemma worse.
3. Having the TV show plots intertwine with the movie plots completely messes up the flow and affects how many people are able to follow up with the timeline of the plots and how they're all interconnected. The diehard fans who watch the shows will know what's up but the casuals who only want to see the movies will be out of the loop.
4. Pushing the "strong woman" angle in a pandering way instead of naturally letting female heroes shine through in the movies. People can pick up on the pandering easily and feel like Marvel is cheapening their brand by doing so.
5. Not giving us X-Men and the Fantastic Four, albeit Phase 5 might follow through with this.