I always viewed it more as the artists trying to depict each of the digimon as if they were angels in their final forms, as in being in a celestial or god-like state.

The merging with humans was an entirely different mechanic. An adjacent evolution line.

Also the majority of the time the higher ranks are just angle/devils which is just human in nature. Most digimon cap out before the last few stages. And remain mostly or entirely beasts.

But when you get to the point where it’s a bunch of gods throwing super blasts at each other… Yeah you either have humanish super creature, or eldrich abomination that is beyond mortal understanding and has no known le shape.

The high ends of digimon get… Wild