Yup, we’ve historically used both rare and elite depending on the context, but you’re right I think I finally cleaned that up to be “Rare” everywhere 
“Rare League” and “Rare Difficulty” still sounds funny to me.
And yes, Crushing Blow wasn’t intended to be the only way you kill enemies. The danger is that if you have enough crushing blow, and it was useful enough, the actual damage you deal doesn’t mean anything.
Crushing Blow is meant to be a supplement, and mostly geared towards PvE.
If anything, I’d rather find some way to have it scale based on your damage or some other investment, but then it becomes just another form of crit.
*Edit: Moving this conversation to a new topic so we can focus on it without cluttering the Q&A thread