I agree with @HubCityQuestion.
Marvel wasn’t ‘racing with someone’ when they started doing the MCU.
They hit a few snags along the way, but they stuck to it.
Endgame is just the reward for persevering and doing what was said couldn’t be done.
DC has had a history of doing a few Batman films, then a few Superman films, then back to Batman with a new actor, then back to Superman with a new actor…
And movies in general rarely went beyond a second or third sequel.
DC/Warner definitely didn’t believe it could happen. Or they would’ve already done it.
Actor pay-rates get too high after a few films, audience turnout declines by the third film.
The only thing feasible to DC was to reboot after some time for the audience to cleanse its palate.
DC then saw Marvel doing it successfully and wanted to jump straight to the reward.
That’s what messed them up.
They needed to wait. Get all the individual characters out there first so they can see what the audience likes.
Apparently Wonder Woman, Aquaman and Shazam gives an indication.
But they already did Justice League. Prematurely.
I don’t think audiences will ever get comic fatigue. No more than they ever got book fatigue.
Now, super-hero fatigue… that’s a different story. Everything moves in and out of popularity after a while.