And percival being human doesn't fit anyways given how potent his magic is.
Humans are pretty much the weakest clan overall, but Ban proved that they are not physically incapable of becoming extremely powerful both physically and magically. Percival could just be someone who has a much easier time actually reaching that level of power.
Alternatively, something I've been thinking about for a while now is how the world used to be in the Age of Light and Darkness, during which the SD and the DK were the strongest creatures in the world and their clans were way stronger than any of the others. As that age ends and the Age of Chaos begins, wouldn't it make sense for creatures associated with Chaos to become the new top dogs? I think humans could be in the process of growing stronger.
To me it sounds weird that anything could come close to comparing to arthur tbh. Arthur isn't merely powerful. Arthur is basically God. Not "a" god like the comparatively worthless demon king or supreme deity. Arthur is just God. Things exist because he deigns them to exist, his is actually omnipotent. He farts out and discards gods like the demon king in his sleep.
I think you're overrating the power of Chaos. We don't know exactly how the DK and the SD were created, but at least in Arthur's hands the power of Chaos is somewhat, pardon the pun, chaotic. There's all this weird stuff popping into existence with seemingly no rhyme or reason. I mean Arthur goes berserk and just tosses a very large die at Meliodas. It's weird.
There are some other interesting details regarding the power of Chaos as well. The most important is the fact that the DK and the SD sealed Chaos away. The creations had free will and enough power to get rid of their creator, so we know that the ability can backfire on the user. Then there's the fact that Chaos was disappointed in the Giant Clan because of their behavior, which means Chaos wasn't able to create exactly the thing it wanted. The power to create things is limited.
Lastly, I could be wrong but I don't remember any clear instances of the power of Chaos directly destroying things. Even Cath was defeated by Arthur absorbing Cath into himself rather than by Arthur just deleting Cath from existence. It seems like Chaos is exclusively a power of creation, which makes failed or rebellious creations all the more dangerous. There is no opposing power of destruction to balance out the power of creation.
Looking at all of these details, I highly doubt Arthur is omnipotent or even close to it. If he was, wouldn't he just wish for his everlasting kingdom to exist instead of trying to make it happen by turning Camelot into some weird pocket dimension? He could even just wish the KOA dead if he's concerned about them or teleport them to him if he's not.
