Bash & Crush vs. Cut & Slash

Well, in reality the reason that with the increasing popularity of plate armor more unpleasent blunt implements were being used has little to do with armor piercing effects. A sword of comparable weight is more effective at hitting plate armor than a blunt hammer and only beaten (haha) by pointed weapons. For piercing armor you need a fine point so something like a pick works best, but when you can't pierce the plate anyway and just cause some blunt trauma, weight of the weapon is the only thing that matters, not if it's hammer or blade shaped.
But it is a lot more expensive to forge high-quality steel for a sword that does not break after a couple of dozen hits to plate armor than to simply put a big lump of iron on top of an oak pole, giving you a functional if unrefined weapon.