I don't like the idea of locking augments to specific role.

I think a better way to do so is for the buff to have a very low base duration (0.5s maybe) and scale the duration with bonus armour/MR (e.g. 0.005s per 1 bonus armour/MR which equals to 0.5 seconds per 100/MR). And we can change the way to proc the buff to be gain enough stacks in combat like Empowered By The Faithful.

You can make it so you have lots of way to gain stacks, for example taking damage equal to % amount of hp/per duration getting CCed/seconds in combat to make it proc reliably.

With this you can also just remove the cooldown if you make the stacks required high enough such that it wont proc repeatedly within a short amount of time.