This question is irrelevant in this context.
It deals warp damage, but it certainly is not a „staff primary attack“.
I guess the debuff also affects the damage dealt with the purgatus staff, but the purgatus staff‘s primary attack can not apply the debuff for what ever reason. Probably bugged.
I’d add that in practice the 2+ talent cost to get there is rarely worth it, but rarely doesn’t mean never:
Channeled Force (+30% to primary after a fully charged secondary for 5s)
Works for all staves (including Purge btw, not that it matters since Purge isn’t used that way)
Empyric Shock is a debuff
This is a big deal bc many of your talent buffs increase base / warp dmg only, with ofc diminishing returns. But EShock’s bonus is applied on top after all your other buffs, multiplicatively.
Warp Flurry on fast staves synergizes fantastically both for proccing Channeled Force and making the most of of Empyric Shock
So any staff builds which regularly combine both fire modes can get dramatically powerful with those two. They do take a bit of time to stack, but Empyric Shock for example makes for a fantastic boss killer. Especially if you combine it with BB, and especially with Empowered Psionics & Kinetic Resonance:
Cap EShock → spam the heck out of your BB’s to max peril → tap primary to refresh the debuff → pop Vent → spam as many BB’s as you can in that 10s period (the debuff & Kinetic Resonance have the same 10s duration).
The issue is more that focusing on bosses isn’t really worth it outside of the last event or some Maelstroms, especially when the talent cost of doing that is so high.