After Avengers: Endgame, the Marvel Cinematic Universe has never been the same, and there are some aspects of the movie that explain how it broke the universe. The latest of Marvel Studios’ Avengers movies, 2019’s Avengers: Endgame, is the biggest superhero movie of all time. The MCU was at the height of its popularity during Phase 3, so when it came time to end the Infinity Saga, Marvel had to deliver, and the studio did so in spades. Avengers: Endgame was the perfect finale to the Infinity Saga, superbly wrapping up the more than 10 years of storytelling the MCU had set up to that point.
Following Avengers: Endgame’s ending, the MCU had to radically change. Marvel Studios was able to release more projects in Phase 4 than it had ever done before — Phase 4 had a mind-blowing 18 projects over just two years, almost matching the Infinity Saga’s 23 movies in an 11-year span — thanks to Disney+. While the addition of TV series and other formats to the MCU allowed Marvel to introduce more characters and give supporting heroes their time to shine, which movies would not have allowed, there was a clear quality drop from Avengers: Endgame to Phase 4’s movies and series. Sadly, Avengers: Endgame contributed directly to the MCU’s recent disarray.
I can think of only two authors who have created worthwhile multiverses, and neither of them work primarily in comics: Michael Moorcock (Elric, Corum, Hawkmoon, etc.) and Stephen King (The Dark Tower). The DC and Marvel multiverses are just a way to stave off the “too many cooks” effect of having dozens of writers doing dozens of reboots of threadbare characters.
tl;dr: Superman should have stayed dead.