LOL HAH NO, daggers were more certainly NOT made to pierce plate. Daggers and dirks were a weapon of last resort....peasants and grunts may use daggers on a downed knight to dog pile and finish him off, they certainly werent stabbing into his plate armor.
Not just peasants, but nearly everyone on the battle field had a dagger to stab downed knights. They'd open the visor to see if it was someone important (to keep for ransom). If he wasn't, they'd stab him in the face with their dagger.
Funny thing with a dagger build though, it requires so much athletics it hardly leaves room for PS. BUT, chambering becomes so much easier with a high speed weapon and high wpf.
I could go on the duel server and chamber a few hits in a row, get a few hits in and then got killed because they started holding attacks.
I'm in favor of increasing the stab damage on the long dagger to something in the 30's.