The new crop of characters and the returning actors prepped to take bigger spots were royally screwed over in all of this. In a better timeline (where this franchise is concerned at least), we'd have had multiple new Shang-Chi, Scarlet Witch, Thor, Chadwick Black Panther, Guardians, Doctor Strange, Captain Falcon, Ant-Man, Moon Knight, Kamala, & Yelena projects with an Avengers team-up film of their own. Time enough to show everyone returning to their element in this new world where the biggest heroes are gone and they have to fill those shoes, and grow as characters' in their own ways, hopefully in a way flows naturally together between each story.
Instead the focus was diluted so entirely that we spent limited audience attention spans on concepts like Celestials, the Eternals, all the conflicting timeline jumping / alternate dimension stuff, half-heartedly introducing mutants and a seperate but equally half-hearted Skrull invasion, planning for a horror-side of the MCU, all while still trying to show Earth grappling with everything post-Snap & Blip. Introducing or teasing characters like Hercules, Echo, the brother of Thanos Harry Styles Star Fox and his CGI troll friend, MODOK, Kang, White Vision, Awkwafina, the Black Knight, all 13 or whatever Eternals, the like 12 different Avengers Babys they were pushing like Amanda, Kate, Kid Loki, Wiccan, Speed.
The initial list I posted is already a pretty substantial list of characters and groups, and more than enough for an Infinity War-sized event film. But when each film or show stacks another hidden realm, another cosmic or extranormal climactic threat, another new set of quippy side characters that will never appear in another film ever again; it all just becomes too much. Especially when the quality and connectiveness just ... wasn't there anymore. It felt exhausting learning about these new concepts and characters knowing that none of these would return or be properly fleshed out. I think more often than any regular person should about how Iron Man got a whole trilogy of films before Avengers 2, and Cap and Thor weren't far behind.
It was always gonna be a tough tightrope to walk for the MCU, post-Endgame. I think the wild success of the solo and relatively disconnected Captain Marvel and Far From Home films, Disney unprecedently incredible 2019 financial run, and a percieved tech-boom gold rush upcoming with their launch of Disney+ ended up swaying them too far from what made the initial phases work.
They needed to make quality films that stuck to those initial characters, added in a handful of fresh faces, and gave them legitimately great arcs and characterization. Keep the lush world-building of early Phase 4 thru each phase. Make it feel rewarding to keep watching.