Two dagger strikes? I haven't looked at the equipment section very closely. Do daggers have a feature that let you attack twice with them as part of a single Bonus Action for Dual Wielding? If there were a way to have them count as a pact weapon—and thus benefit from Lifedrinker—and if you could get the Dual Wielding fighting style without sacrificing your capstone, that's a really solid boost to damage.... oh.
So. Dual Wielding is a thing...
Thirsting blade Longsword+Dagger at 20.
4 Eldritch Scythe Swings, 1 Longsword, 2 Dagger Strikes as a Bonus Action.
... and a partridge in a pear tree.