They are very fast, they have relatively decent range and good burst, and they have absolutely godawful DPS, are made of papier-mâché, and tend to take losing trades against anything they can't overwhelm. Daggers also don't maintain relevance very long into a typical game.
A lot like blitzes, honestly- given the right fight, they certainly
look overpowered, but there's a reason you don't see them spammed the way people will spam glaives, bandits, or ducks, and they don't even do the early game as well as a good kodachi.