There is the combination with Sneak perks. I'm working on it now, and if I remember correctly it goes up to fifteen times damage for a sneak attack with daggers. I think that makes them very powerful.
This. x15 sneak damage makes a regular dagger hit like a bus, and anything better hits like a nuke.
Daggers aren't meant to be used in a knock down drag out fight against atronochs and mega draugr.
They are meant for sneak attacks, and killing smaller enemies.
Use daggers 'till your stealth is broken, then have something bigger to smack them around with.
My primary is a bow. In my right hand I keep a heavy hitting long sword, and in my left a dagger of
my choosing. I usually have the dagger with some sort of special effect like fear or paralyze.
This way I can backstab when needed, or use it for crowd control in a stand up fight.
tl;dr- save the heavy fighting for swords.