The longbow did more to remove full plate armor from the field than any other weapon in history.
Rapier? I laugh at you. A bludgeoning weapon to the skull would strike deadly blows as plate deals with bludgeoning damage terribly. It does little to absorb the blow and does not give at all, therefor translating that trama to the person inside the tin can.
Seriously though, most people in full plate died from either piercing weapons such as spears or arrows, or even moreso, slices to the calf region on the back of the legs. It is very difficult to make full protecting coverings for that joint in the body. I've seen some very well documented papers on the subject through the SCA, and a short sword to the joint in the back of the knee can either lead to disablement, infection, and then eventual toxic shock trama or just sheer bloodloss and ultimately death. Once the armor is bent and twisted, it is near impossible to remove without mangling the limb.
When a phalanx line was used pikes, arrows, and lucky shots with thinner durable blades (such as rapiers) hitting chinks in the armor did the killing, with one on one combat it was disablement of the legs or sheer blunt trama that won. Think
Ajax and his giant frickin rocks.