I think you are missing the how
rapiers and other light weapons (
small sword,
epee, ect) were brought into fashion.
Big ass armor became
obsolete when
gun powder became prevalent. If a hand gun will punch straight through 60 pound armor, then wearing that all that crap becomes useless. Then comes the importance of light and fast weapons.
Rapiers and such would be nearly useless against a heavily armored opponent. They would be hard pressed to parry a heavier sword, and if the armored fellow knew what he was doing (didn't give flat shots to the rapier guy) it would be near impossible to poke a hole in him. Angle of deflection and all that.
Put the smart money on a light weapons fighter with a pistol of course, but don't count out the heavy armor in a stand up fight.