I think the issue is pretty simple. IMO.
It's another replay of the old, "Goose that laid the golden eggs." To put it simply- Disney used to understand that proper brand management also meant scarcity. Too much of a good thing can ruin it. And that's what we've gotten.
During the Infinity Wars saga, you would get two movies a year. You would only get three movies if there was an additional Spiderman movie (done with Sony). That's it. Each movie was a big event.
But now?
2021- Four movies.
2022- Three movies.
2023- Three movies.
2024- Three movies.
In addition the upping the amount of content in terms of movies, they have also, at the same time, ensured that there is a firehose of content on Disney+.
2021- Five shows (counting What If?).
2022- Three shows.
2023- Two shows.
In addition, they've tied the shows into the MCU. So if you're "into" Marvel, it starts to feel like homework. And if you don't watch the shows, then you feel like you're missing things. Also? If you are "into" Marvel, you know that the movies will be on streaming soon, lessening your desire to see the movie in the theater.
It's just a firehose of content. And the quality has suffered because of the need to make so many shows and movies at the same time. -The VFX has suffered. The shows exist in some kind of bizarre space- not really TV shows (most don't have a second season), and not really movies either. The stories have suffered- you have "old" characters in completely inessential shows (Secret Invasion), and new characters in great shows that just end (Ms. Marvel) and make you wonder why you took the time to invest in such a great show to begin with ... because it's not a show.
Moreover, the MCU has lost the "event" feeling. I genuinely like two of the three characters in the Marvels. But the movie is barely a blip on my radar, because it's just another marker in the firehose of content. I'll probably watch it at some point on streaming, but I don't feel the need to see it in the theater.
TLDR; the MCU has suffered because they made too much, too quickly, and now it no longer feels as special as it once did.