No one is demanding highest form of art from MCU , theres a middle ground . A middle ground something like Nolan batman movies, like Logan , like Joker. The craft behind those films , the performances and the overall approach to story telling has far more substance . Even outside comic book movies , MCU has a lot of action but a lot of it ranges from solid to barely competent. Movies like Fury road , recent mission impossible films , even lower budget stuff like Raid films or Dredd. Theres craft and pride in making high quality action films . All of em arent high art cinema, they are action blockbusters, but those same films show the level of quality in their execution.
What about Kids films ? How to train your dragon trilogy is one of the best modern kids movies in recent times . Tangled , Frozen, Toy story movies? They are all high quality movies that are aimed at children, but theres no denying about em as a piece or entertainment .
Why MCU , of all things, with all the hundreds of billions of dollars from disney cant strive to be something more? Why Black Panther , probably one of the most important superhero movies in this decade or ever for a significant portion of people has to have god awful cgi fight in third act? Why End game , the ultimate end of a saga that has 20 something movies spanning decades had to have obnoxious fan service and a drop in quality when it comes to fight choreography and set pieces compared to Infinity war?
Marvel and Disney are okay at dictating the modern movie making and having nearly every movie that comes out making a billion , so its only fair to criticize if for not doing something more , because they have resources , because they have talent behind these projects .