Mitigation, if we were to talk as it is defined, seems like it would be how much damage the shield actually cancels out. So, if its say 25%, and theres 100 damage, the shields cancel out 25 damage, so the actual shield depleting damage becomes 75.
I think thats what Baleur was trying to say, but i figured i'd punch in with an overly complex and redundant way of saying it

Tec has armor bonuses too, doesn't it?
Seems like the tec get the good armor/repair bonuses, the vasari get the mitigation and decent shield power bonuses, and the advent get good shielding strength/recharge and weapon bonuses.
I could be wrong, just how it seems.
ps, i've been playing for maybe 4 days, heh. I was in the beta, but beta vs retail is a pretty nice leap.