There was, is(?), a plan they had shown many times how things were planned out 10 years in advance detailing where they wanted to go. Now did they stop following the plan or became complaisant maybe I can see that. The plan also likely got more difficult as they went from the Avengers only to wanting, fans wanting, them to add the Fantastic Four and mutants/X-Men. Maybe they are taking too long to get to those characters but at the same time they wanted enough time between the FOX version of those characters and their new version I guess.I'm not sure there ever was a formula.
They made movies about superheroes from 2008 to 2012 and kept the door open to making more: the first Avenger movie tied up everything that had been set up, the MCU could have ended there because they made it so that it could be (Thanos post credits was keeping the door open).
The Infinity Stones saga was a huge hit so then Disney behaved like there was a formula but what they did was "set things up and go from there" not "lets plan everything from the start every 10 years".
This isn't super hero fatigue, it is huge brand fatigue.
Trying to connect it all is likely one of the biggest issues along with continuing to include smaller characters that are much less known even to comic readers.