If you want it even more accurate to CoH, recall that Defense and Damage Resistance were two very different stats, where defense determines how hard it is to actually hit the target, and resistance is factored in if a hit occurs.
Depending on whether or not you're including different power sets, I'd say Scrappers could potentially have a higher defense than Tanks, while Tanks have a higher damage resistance, as just one example.
As a consequence of this, you would need to do toHit rolls in addition to actual damage rolls, not too disimilar to most pen and paper games I imagine, but of course different ATs would have different accuracy bonuses to offset this, such as Blasters having the highest accuracy for example.