At least The World and The Vault get mentioned and remembered. Meanwhile The Hill is sitting in a corner crying because nobody cares about it, despite it having the same role as these two.
Accelerated time compared to the normal universe? Check. Weird hostile environment (acid rain, techno-organic flora and fauna, sunlight burns like lasers, rocks floating in the clouds, atmosphere causes rapid regeneration, etc.) that tests the survival abilities of anyone who lives there? Check. Used for an attempt at breeding stronger super humans? Check.
The Hill can even claim to have been there first, but even now that Mikhail Rasputin is back as villain The Hill doesn't even get a passing note as any place of interest.
Though it certainly didn't help that the "super humans" produced by The Hill were Gene Nation who unlike the Children of the Vault or even The Neo were never hyped up by their creator, since they their entire role was just to put Storm into a place where she had to stab a fool to death again. So right from the start they were settled with being just a bunch of "angry youths" rather than hardened survivalist their story was supposed to have made them.
Overall though i agree that it certainly doesn't help any character to have been born in or be tied to a small self contained small world which is entirely based around producing them and with no larger connection to the Marvel universe.
Because unlike Mojoverse, Otherworld or Limbo, who have roles and activities not tied to the characters originating from them, the Vault, the World and the Hill have no other role but produce Weapon Plus subjects, the Children or Gene Nation.
While Fantomex is still quite successfull (which i never quite understood), it can't be said for many other characters produced from his kind of origin.
Of course the Children of the Vault could still have a larger role in the current Hickman run, but it doesn't look like they have much of a chance to stick around once he is gone and the next status quo will likely get more grounded again.
As for Genosha. Looking back, i once again have to notice what a massive waste it's destruction was and how it in my opinion taints any positive story aspects from the Morrison run. Because it leaves behind a legacy which not only brought down the x-men world into a further thematic darkness than it had allready been (the constant extinction storylines and "humans vs. mutants" narrative) it still hasn't recovered from, but also still breaks my willing suspension of disbelief (yes in a comic series about people born with super powers), just for how little it left an impact on the Marvel Universe.
The destruction of a whole nation with the death of 16 million people in a few minutes, should be a big deal, even for a fictional nation in a super hero universe. Especialy since it wasn't some "hidden" civilization, but an openly existing state that had been a subject to several actions by the UN.
What ever the narrative tries to present the entire world as hating mutants, the reaction should have still been shock, disbelief, anger and especialy questions and not just by mutants but humanity at large. Because even those who would welcome it's destruction would be keen to know where the weapon can from, who made it and how it could be countered or reproduced. Because if there was one massive mega Sentinel which could wipe out an entire island nation, there could be more and next time they could be destroying their country.
It didn't even do good for the X-men, since while some writers liked to play Genosha as the victim card against other Marvel heros the X-men were just as apathic towards it as the rest of the marvel heros.