I think that this has always been (one of ) the problem with herald. When people talk about herald's sustain, they all refer to this specific skill. The ability to heal more than someone who is built for heal is beyond me. It was like having a better version of reflect which not only reflects all projectiles but all incoming damage. Just imagine how toxic that skill would be. But never mind...
The drawback of such skills like defiant stance is longer cd (30 secs) compared to other "regular" heals (20-25 secs). Rev is the only class that should not have access to this kind of skill because they already have 2 healing skills which in practice makes infuse light only have 15secs cd. This is why I suggest:
-either change the whole skill so that it doesn t convert all incoming damage in heal anymore
-either make it 45 secs cd to match up with other similar skills I mentioned above.