Except that's not fucking true. If Guzzlord were responsible for destroying the world. If they were violent, destructive, and not friendly at all? Why would the only human left stay behind to be it's friend? He clearly refers to "Mr. Glutton" affectionately. He asks you not to touch his food, and seems saddened that they are starting to die out.
Guzzlord isn't evil or violent. Dangerous maybe as one ate a person in SM when it was scared and threatened, but they clearly aren't the most dangerous Pokemon canonically and they almost definitely didn't cause this disaster. They are just big, strong, and endlessly hungry. But they seem to be reasonably friendly.
Fuck Celesteela is far more dangerous. They are a parasitic organism that flies to a planet, reproduces endlessly consuming it's landmass and nutrients/energy, and then blast off to another one to start the process over again. So even if Guzzlord DID do this (I doubt it) it only ended ONE planet when Celesteela have likely ended many.