The Marvels failed because people don't like the Ms Marvel character and don't know the other two.
Captain Marvel was a solid origin film, establishing the lead well enough that a proper sequel focused on her was rightfully expected...yet that did not happen, and even Larson was not particularly happy with choices made for the sequel.
Eternals failed because nobody knows the characters and unlike Guardians you don't have someone like Gunn making the movie and the movie gave off the vibe it was going to be slow,pretentious and new agey where the Guardians move was basically selling itself as Buck Rogers or Farscape and it was going to be wild and crazy and fun. Love and Thunder came out when Marvel fatigue was just starting to kick in. Plus bad word of mouth.
Pretty much.
Finally Brave New World was a Captain America movie without the Captain America people love. Instead it starred his sidekick.
Any dedicated followers of the MCU--well, the
rational MCU followers accepted Evans deciding to leave the role in
Endgame, which simultaneously passed the Cap I.D. to Mackie's Wilson. This was not a surprise casting change dropped on audiences, but an evolution of the Cap end of the MCU set up for some time and officially settled in the D+ series. That said, anyone still having issues with Wilson as Captain America only reveal their true problem, the kind so often spewed on YouTube channels such as Nerdrotic, The Critical Drinker, Geeks and Gamers, Ryan Kinel, The Quartering, Heels vs Babyface and platforms hosted by illiterate, wannabe anarchists such as Charlie Kirk and Tim Pool. In other words, if Captain
America does not fit their unironically Third Reich-esque idea of the blond
ubermensch draped in the American flag (a Marvel internal problem addressed in Cap comics of the 60s and 70s, but completely ignored by the types cited here), then
"there is no Captain America" and
"...this is not what WE want to see".
Disney has made some bad choices not just in execution but also the things they have selected to make. Not to mention putting to much stuff out their to fill out it's streaming service.
Ever the historically proven act of self destruction in the film entertainment business: quantity over quality, and the #1 culprit of that in the superhero movie genre is the MCU. As many MCU entries from film, network TV and streaming exist, the majority were/are not great, memorable productions. They were and are just more assembly line product with little creative value, rather than what it should have been: a tight number of films which poured the best of the source (with some expected changes for film), which does not walk in lockstep with 25-film/TV arcs and set-ups for endless spin-offs.
A few films with a running plot (e.g. the aforementioned Cap considering his place in life / passing on the Cap I.D. to Wilson) were fine, but that's the outlier approach in the soap-opera-esque, "everything everywhere is connected to the Big One" handling of the MCU.
They have nobody really to blame but themselves.
Obviously.
Now it's time to see if they can fix the problem or not. Odds are it will become more hit and miss and not as consistently successful as it used to be.
Probably the case.
But now and then they will still have a big hit. The next Spiderman movie for sure will be successful.
We will see.
As will the Avengers movies if for no other reason than people want to go see Robert Downey Jr again in a MCU movie.
If there's merit to your theory, it would have more to do with certain, irrational members of the MCU / moviegoing audience still thinking Dr. Doom will have anything to do with a dead character, instead of accepting a long-lived Marvel antagonist as he was meant to be.