With the exception of Cygnar all Armor buffs are really caster dependent and most buffs can be removed. So to say Conquest has usually the least Armor and is the least durable is really making a whole host of assumptions. I could say he's the most survivable because the mechanics can just repair him up, but I'm not going to make that claim with no play testing to back it up and the same should go for the reverse.Reminder: Conquest is the least durable Colossal, with the lowest DEF, usually the lowest ARM, and while the box counts are quite similar, the second highest box count. If you field him, you should be protecting him like you would a hundred dollar basket of eggs.
At this point as far as durability and survivability go all we can say is he's 19 points out of your list put something in front of him for Pete's sake,