The fact the 95% or more of all dragons are not going to ever use it (that even obtain one, no telling how long this event will be in, they may become un-obtainable at some point in the near future), should tell the dev's something. As rare and hard to obtain as it is, why can't it be useful alongside something like vengeance?
Even with that scale and a vengeance scale, dragons are not going to be invincible, and are still going to die alot. Hopefully it would be a bit less with the scale.