have you ever actually looked at the armor ratings of most PVE enemies? The only boss I ever found where armor pen made any sense over raw dmg is the arena champion.

And why compare specifically those 2 unrelated weapons?
At least compare Dead Leg with another 2h Hammer…like Hanuman’s Gada.
There are a dozen better legendary 2h Maces in the game, all vastly superiour to Dead Leg. It is not just a difference of 10 to 15% less dmg, since without a bladesmith, which is one of the rarest thrall to get for some reason, you are looking at a 20% inferiour weapon. That is basically a whole tier lower.