UNSC is the overpowered civilization...heres why
UNSC and Covy both have their special unit aka gremlin, brute, cyclops etc
UNSC both have powers aka vortex, cryo bomb, rage. (UNSC has more advantage here than you think, the covies can only use their leader power near their leader, UNSC can use theirs anywhere they have a unit.
Here is where the covies start losing
The UNSC has a second special unit, grizzlies, hawks etc.....massed hawks be countered by nothing but vampires, and even when you win that battle your left wth a unit that can only kill one thing and sucks against everything else.
and the last advantage they have over covy is the economic boost.
The game is pretty balanced as is right now. Yes there could be some improvements but i wouldnt listen to 90% of what the lil kids say that come on here and complain about how they got beat and suck and therefore a faction is overpowered.
Things i would suggest changing
Either slow the arbiter down so he can at least be targeted by enemiy units or just make him a lil weaker
make hogs count as 2 pop or make ghosts count as 1 pop, its ridiculous that a one seater ghost takes more pop room than a three seater hog.
Make the cheiftan as good as the other leaders, as is, the prophet and arbiter own his butt head to head evertime.
Make turrets worth building, as is, they are a minor inconvienience.
Possibly tone down the hawks a lil bit. iether make them cost more, or make them weaker.
Brute Chieftain FTW