meh the orca bomber is pretty over powered but thats why in normal TS Nod had the nice artillery for their over-powered unit.
really i think the Orca B is a little too fast for its nature of being a heavy bomber but a lot of sams and say good bye to them with ease. i guess that goes with all aircraft though. but Banshees work wonders in large groups really.
also......if you want to see overpowered...i once took one of the voxels that was "scrin" like from here...(i forget who made it or what it was called) and i gave it the tag
ammo=-1

now that was fun.
personally if i had to put 2 overpowered units for each team it would be something like this:
GDI
-Disrupter
-Orca Bomber
Nod
-Artillery
-ermm crap.....maybe the Cyborg Commando....although i really wouldnt consider him overpowered as hes a special unit you can only get one of and the Ghost stalker technically is equal to him...
but really these are only over powered when used in large numbers just like any other unit.
now under powered...thats a whole other story. GDI-APC (cause it kinda sucks compared to the Subterranean one plus the original APC at least had a gun) Nod-Devils Tongue