Martial combat isn't about who has the most damaging weapon man.
You could kill someone in full plate with an ice pick. Would you have to disable the foe first, beat them down? Yes, 100%. But a hammer, mace, whatever, doesn't just shatter a person on the spot when you come near them either. They'll fight back. You'll still have to disable them or get them into a weak position to muster the force to beat the air out of them, and to successfully hit the money spots to do so.
Furthermore I'd bet if you wanted to kill someone in full plate, you'd get them on the ground and finish them with a knife. Regardless of what weapon you beat them with. It's just quicker.