So to reiterate, Pucci isn't destroying the universe with his own power.
Except he is? You're being semantic with the cause, while ignoring the fact that he quite literally does cause the universe to end under his own power. Completely ignoring the birth of a new one.
He's accelerating time using gravity and abusing relativity to speed up the reset process that would have happened naturally even without MiH.
That's a half truth, ignoring the fact he'd have 3-A ED with said gravity manip regardless as that's straight up stated to be on a universal scale and can effect time itself, it's not a complete natural occurrence even with the end result, even if you want to say that "well he's just speeding it up so it doesnt count", the way it happens isn't even natural, the acceleration is disproportionate to how it would be naturally and instead correlates to the acceleration of the time, it's why things have such jacked up KE. And things don't crumble naturally as if over time but instead violently. Even at worst, it wouldn't be natural in process but fast, but more forceful if anything and disproportionate to what it should be, not what it is.
So MiH wouldn't scale to Low 2-C AP.
Still qualifies for Environmental Destruction, hate to be that dude but, all these roundabout caveats and stipulations and even requirements everyone is pointing out needs to happen, don't actually exist on the ED page, it doesn't matter how it happens or comes about, as long as the character can cause quantifiable destruction to the environment and under their own control, that shit is ED. The fact this isn't just simple time manip makes it doubly so.
Also as for your gatcha example.
and is abused by Pucci in Part 6 for the express purpose of finding a universe where the Joestars don't exist.
That's literally not true though?
He CANT abuse it for what you're implying, it's actually impossible. He wanted a world without the Joestars, but the way he was going to obtain it isn't him rolling a dice and praying this reset doesnt have any, in fact we know that's not the case, if Joestars were still alive, they'd be sent over to the new dimension just fine such as Oldseph, Josuke, etc and if they're dead, they're be replaced with a duplicate, as we see with Jotaro and Jolyne, albeit, one that lacks the original soul.
How his ability works outright makes what you're suggesting impossible to happen, he can't roll a dice so it never happens, he has to kill the Joestars himself so they don't get brought over, which is why he stops to kill Emporio, as while not a Joestar, he still considers him something he wants gone and not in his new world.
No matter how many times Pucci tries, he will never get a universe where Joestar anything doesn't exist, not even duplicates, as that isn't how it works, and he knows it.
Pucci has to keep resetting because he can't control the actual universe that is being reset and has to gacha it.
That's, not true at all? Literally all he wanted to do after the first reset was kill Emporio because he wasn't supposed to come because his Stand explicitly relocates the living into the new world. After he killed Emporio he was fine because all his bad connections would've been dead and gone. He wasn't gonna just roll a new universe ad infinitum, in fact, it wouldn't of done anything because that isn't how the Stand works, """"Joestar expies"""" would've been in every new universe, this ain't D4C where he might get lucky, it'll happen every time and that's the whole point, everything is SUPPOSED to be the same, that way everyone will have precognition to what will happen, that's his true goal, give everyone the ability to see the future to come to terms with destiny.
And oddly enough, Pucci is the single person who CAN control anything, he's the only person not subjugated to the fate and events happening, he can change things as he pleases, to his benefit and detriment, such as when he changed Emporio's fate, which ended up killing himself.
Honestly, even if it was purely just time accel straight up, I'd say due to how it acts in function and in action, it's functionally enough to qualify because like, come the **** on.
That's a bit much to just go "eh doesnt count". Especially when Pucci can flip it on and off and do ad infinitum whenever he wants.