Was playing around a bit with the mod in testing environments and noticed the units don't have walking sounds and big units sound like small units.
Also, their scales are not what I remember (I imagine tier 10 to be huge monstrosities like in the original Rampant mod).

So, just now I took a look around the Lua code and found that in "prototypes/utils/BiterUtils.lua", the makeBiter function never sets the "walking_sound" for the unit.

I originally discovered, through the prototype inspector thing in-game, that Rampant enemies have no walking_sound (show as "<empty>")

In addition, the biters roar are not accounting for the tier, so even large units sound like the small units, just louder, I guess?

I hope this conveys my observations clearly. Maybe this is a bug? Not a bug of the AI, but of appearance and audio, I guess.