What I've tried to do with units is not necesarily to tone them down, but certainly to give the nations more counters and answers to things. Empire now has the option of mercenary Tilean Pikemen who provide a VERY solid line against Chaos, plus next release the Empire will have extra troops for harassing or blowing up the Chaos Horde. Empire may never be the strongest faction, but they will have more troop options than almost any other race.