“Prof X had them hidden” is some stupid shyt.
So mutant villains were just gonna be chillin on the beach while chaos was happening? No X-Men for backup when Ultrob showed up?.
I’m just spitting out how I can see it done differently. I’m a comic book head and been watching CBM since Tobey was Spidey. I’m not gonna go on over fantasy booking.
The Eternals are all superpowered, the movie came up with a reason/storyline to not have them get involved with the wider mcu and previous events.
"The Winter Soldier" didn't exist as a character until the mcu's 9th movie and was retconned into the mcu's in movie history and then in Captain America 3 made the killer of Iron Man's parents.
The same can be done for Mutants or it could simply be a case that only now mutants are emerging in numbers, the point is that's it's not as hard or as complicated as y'all make it and it doesn't require any sort of "reset" or "reboot" to integrate them
That's why Namor and Ms Marvel are already in the mcu and are mutants.