Perhaps they could make it work more like skills such as the NB shade; activate the skill again within a certain time frame to toggle the purge. Even without Plaguebreak's presence, it seems only fair that the player would have to actually do something for the purge, even if it is just an extra button press.

Then again, I don't play Warden in PVP, so take this as an outside perspective.

Honestly, when it comes to problems regarding the interactions between sets and skills, I'd rather see the set get fixed/changed than see a skill get changed because of the set. Even if I think the skill could use a tweak, that tweak should be for the sake of the skill and how it works in the class. Not because of a set.

Plaguebreak also just simply has too easy of conditions to meet. Deal direct damage to apply with a 100ms cooldown between applications. For the power it can offer, it needs stricter requirements. Less ease of application, a longer cool down, and a trigger mechanisms that doesn't punish using crucial identity skills for several classes would do the trick.