ok, I see your point, although it might be noted that in the current game, towards the end anyway, Scourge, Fury, and Domination (when perma) are all basically passive.
However, since I was envisioning this as a support focused archetype it seems like, similar to Defenders and Controllers, a passive inherent is acceptable since Buff sets already tend mostly to be Not very passive.
But I see what you mean, the game's design did evolve somewhat.
Ok, so here's my thought process in regards to this idea:
The Buff sets are already some of the most fun powers in any MMO. They really don't need much alteration.
I didn't want it to be Defender-lite. I wanted it to be competitive with Defenders for team support. So maybe that's not clear in the OP.
Corruptors are already more redundant, it seems, since they literally have the same powers.
Soooo...maybe if instead of passive mez protection and shielding they got a tiny stacking mez protection (and maybe some kind of shielding) buff each time they used a Primary power?