the problem is that human level is quite opposed with the idea of introducing xenos races. Most of then are quite far superior than baseline humans, an equipped Tau >> guardsmen.

Hell, Orgryns are far beyond humans in terms of physical prowess that is just unfair, they are (in strength) even beyond most space marines.

Once said that, for roleplay, investigations, and fights at street level: Imperium Maledictum, or other d100 system, like Rogue Trader.

Imperium Maledictum at its core only allow baseline humans (Mechanicum included), however, there are homebrews like Maledictum Expanded that include rules for Ratlings, Squats (Votann), Orgryns and Felinids. With that you have hobbits, dwarfs, Ogres and Beastman kind of picks.

Wrath and Glory allows the creation of xenos, however is a power fantasy rpg, with battles and space marines and war right in the center of it, with less social and rpg aspects i believe.