In my opinion the MCU is fine. This was always bound to happen after the Infinity Saga. It was literally 5 months ago that Doctor Strange grossed 940M. Imagine if people actually liked the movie. The MCU was always going to stabilize downards after Endgame. It lost China which seemingly nobody wants to actual factor in and China was huge for the MCU in terms of grosses. I don´t know how we can say that these movies are only watched by fans when they get to 800M+. Wakanda Forever was always going to drop from the first one and it pretty much has everything going against with exchange rates, world cup, lost it´s lead and all that. Tho I hoped it would have hold stronger.
I wouldn´t say 800M-900M is anything amazing rather it´s OK result. I think that the movie was liked by the fans is more important than any other thing. If this would have gotten same reception as Thor and Mom then I would really have been worried for Ant-Man 3. Now the two latest MCU projects have been received well. But the days of MCU churning out 1B is over.