You mean rare enemy.
That makes crushing blow absolutely useless…
An epic enemy would need 30 crushing blows to be dropped to 89% hp and approx 180 procs of crushing blow to drop to 50%. That would be 6 solid seconds of attacking for it to even drop to 50%…
You should really adjust the scaling to something like
Crushing dmg % = (current hp %)*(1-0.25^(rarity lvl/2))
or it would take you forever to kill enemies.
With that formula you would have to cause 11 crushing blows to get an enemy to 50%.
You would have to tweak the /2 at the end of the formula a bit (maybe to /1,5 or /1,4) but with the current formula it takes forever to even kill epics.