What I think is funny is that plasma weapons probably don't have the same power as 400 H-bombs, which is what you need to destroy a CAIN!
Soooo.... How much weaker are they? (Great, WTF is a DU? Damage Unit? OK.....) So... A perfect hit from a Fuel rod gun is weaker than a plasma grendade, a plasma grenade is.... enough to kill an elite, with shield, which sends him flying 3m up, which means... bah.
Yep, lesson learned, don't compare universes. Especially when scale is screwy, damage is in funny numbers, etc.