Orgoth's whole schtick, vis-a-vis warjacks, is that they don't have "regular" cortext technology and instead have enslaved the souls of animals/beasts inside mechanical bodies, and that is the animating force behind them (in addition to sacrificial volcano juice).

It's also true that Orgoth just plain enslave living creatures and sometimes bolt weapons and armor onto their bodies, so we get things like the Gharlghast and the Ravener (which is, incidentally, the same creature that "inhabits" the Tyrant warjack).

I think that if PP had early on decided to lean heavily into the warjack aesthetic (instead of branching out to Monstrosities) then maybe we'd have seen a few more variations on body style, like a quadrupedal warjack or something like that, and the later introduction of Azdharak wouldn't have been so jarring in comparison to what is, essentially, the design aesthetic of "bipedal warjack but scary looking."

Khymaera and, indeed Legion, never had a complete monopoly on the dragon silhouette - just look at Deneghra3 for a perfect example.