(DW as in Duel wield)
(Power attack as in holding down both keys)

My all time favorite classes are stealth-based and I love daggers, but the dual attacks feel so weak & slow

Try going from 2x swords to 2x daggers.
I don't even think elemental fury affects it at all.

It was so slow that I changed to nightblade (spell+dagger)

I'm pretty sure there's a bug that screws up the DW power attack with daggers that makes it so slow. The DW perks that boost speed don't affect it either.

I hate it too.