I haven't been on PTR at all so I can neither confirm nor dismiss Deterrence as being a nerf. However, at one point GC said that Deterrence will get 2 charges on every cooldown. So after 3 minutes you'd have 2 charges to use even if you used up the 2 charges 3 minutes ago. I haven't seen anyone confirm that this is how Deterrence currently works on PTR so it is possible that it will work like the normal charge system does and just award 1 charge everytime the CD finishes in which case it is a substantial nerf to our only defensive CD.