The MCU has plenty of steam left, and will see many highs, but I think it is safe to say it has peaked with Infinity War / Endgame. It will continue to be a very successful brand / franchise. But it is moving into a somewhat more diluted phase. Some folks will hop off this train now that the original characters stories are finished. New kids will jump on, but it's becoming time to turn the page, something else will be the new hotness within 3 years. You won't be able to predict it, just like how Harry Potter seemed to come out of nowhere. (A good live-action Last Airbender, please!)
But even in the 'dark times' of the Star Wars brand (late 80's - early 90's) Star Tours was still a super popular attraction. Temple of the Forbidden Eye opened with Last Crusade having "finished" the Indy franchise 6 years prior. Marvel land will do just fine even if they don't ever make another Marvel movie (which definitely isn't the plan).