In my experience, the most OP race of all are the Scavengers. I have yet to play a scenario where they are present and everyone else does NOT get steamrolled by them
It feels almost critical to side with or wipe them early on.
It would be nice if there was a little more balance between races, yes, but i guess the cannon fodder needs to be. Dryad, Lithosoid, Shadow... they're pretty much filling, always on the losing side.