on a nitpicky note rapiers are actually incredibly effective against articulated plate and along with crossbows and firearms led to its eventual disuse. The point control is such that you can strike the joints and the tip of a rapier is actually structured to be more effective at piercing even a solid plate than a standard broadsword for instance.
So long as you're talking about an actual rapier, and not the smallsword that Errol Flynn and stage fighting have put into the public consciousness as a 'rapier'. The actual period rapier weighed roughly the same as a standard sword, after all, not the featherweight wrist-flicking thing that movies love to show.