I've played all three races, and I do have to agree that Orcs seem a little underpowered. I've yet to find a way to use their strengths as well as I can use the strengths of Elves and Men.
With men I apply superior cavalry to the enemy's weak spots.
With Elves, I set up a hard line with heavy infantry to hold them at a distance, then rain down arrows with superior archers along with flank attacks from hidden units.
I've yet to figure out how to use the Orcs correctly other than throwing ogres at my enemy.
--In Game: Erebus