While the Eternals are long-lived and are conventionally good-looking, the Deviants look monstrous and their special abilities aren’t as great as the ones the Eternals boast.
For those unfamiliar with Eternals lore, the Eternals and the Deviants were the products of genetic experimentation conducted on proto-humanity by the powerful Celestials one million years ago.
Evidently that won’t be the case for Kro, though even if you exclude him, the Deviant are able to somewhat able to level the playing field by having greater numbers and their own advanced technology.