The problem I have with tanks is the lack of armor. At best I had one get up to 35% which is easily cut down by mobs that shred armor (armor rating debuff). When they drop to 20% they get cut down fast unless you can heal them, they also have a worse rating then even my cloth wearers at that point. I think they really need a armor boost in their tanking stance like a player does.
Wish they would have more advanced control of the companion AI too. Would be nice to tell your healer to hold a position and also to keep his damn gun in the holster