This is a diplos primary fire build, due to its alt fire being awfull (the lock on mechanic). It is still balanced enough to use the secondary fire. Keep in mind, that due to [Galvanized Shot] being bugged in the diplos, as it acts as a multiplicative bonus on the alt fire instead of additive to [Hornet Strike].

Primed expel boosts the slash procs (double dips) , that are able to proc due to the high fire rate, even if viral has a much higher weight (in higher levels leave 60 cold unranked). [Carnis Stinger] is used to boost the slash weight a bit alongisde with the status chance.
The arcane used is up to the user. Dextery is the one with the best passive for secondaries, as you won't be killing fast enough to keep merciless up nor achieving headshots reliably to keep deadhead on (its incredibly hard to achieve headshots with the alt fire aswell)