Using throwing dagger completely removes a melee combo attack from your timeline, Raiton just swaps one in for the Raiton in Trick.

Your melee combo attacks average out to around 320 potency per hit (+ 5 additional Ninki from your finisher), so you're losing over 200 potency.

Also keep in mind that you can't fit a third Raiju into Trick during 120s bursts, so you're only gaining the 5% from Mug + any other 20s buffs.