It's a structural problem. The MCU is very Avengers-centric, whereas the comics never were. It's true that for many years Iron Man and Captain America took turns being the lynchpin of the Avengers, but outside Avengers mansion, they had less pull.

The X-Men, for instance, had different concerns, as did the Fantastic Four. Spider-Man forged his individual path. Dr Strange confined his attention solely to the magical. The Hulk was a force of nature, etc.

But by centralising Stark, SHIELD and the Avengers, and making their connections with others stronger, the MCU left themselves vulnerable to the inevitable departure of actors from roles. Unlike The Doctor, Stark and Captain America cannot 'regenerate', though their suits can be worn by different people.

The biggest mistake was making Stark Peter Parkers' mentor. It basically took away the fact that Peter, as originally written, was as brilliant as Stark or Reed Richards in his own right.

It would be better if the MCU now concentrated on the separate paths of its various groups and individual heroes for a while.