It's very weird, the narrative being constructed here. At least in movies, the facts don't support the implied claim. (And in TV, there's not much to compare pre- and post-Endgame.)
Of the top 10 MCU movies in worldwide box office (aka the ones making over $1B), three were post-Endgame. 3 in 4 years versus 7 in 11 (since Iron Man/Incredible Hulk).
In the next group of 10 (down to $676M worldwide), 4 were post-Endgame. Again: that's 4 in 4 years versus 6 in 11.
This means that in the top 20 MCU movies, 7 were post-Endgame. 7 in 4 years (1.75 per year) versus 13 in 11 (1.2 per year).
I think... I think they're doing fine...? In the real world, among real people, most of the things the article points out (like the CGI quality) don't rate a second thought. They just don't care. Did they have fun? Yes or no? All the little detail bullshit that the chronically online like to harp about is just not important to the vast majority of moviegoers. They do not fucking care.
What could be argued is that things have dipped from 2021 to 2023, since none of the 5 movies from the past 2 years have cracked $1B and only one cracked $1B in 2021. But that's not "post-Endgame" that's "mid- and post-pandemic." Not exactly the same thing. Can we at least admit that the most world-changing event of the past 80 years might actually be more responsible for any perceived "break" than something as nebulously undefined as "superhero fatigue" or as ridiculously unimportant (to most people) as "marginal drop in quality"?