Totally Agree, the gem will ruin the game, otherwise please give frost mages a PvP talent so our spells don’t slow and give the kill target a permanent 15% wall
Assuming it works like echoing resolve (there’s no auras datamined yet) it will only work for full cc - horrify, silence, trap, poly, clone, fear, stun.
No changes to CC would ever be necessary if damage had been kept in line. WoW PvP changes since BfA S4 are like using a fire extinguisher on one’s flaming bed while the kitchen stove is what started the fire and the entire house is burning and crashing down.
While slows are a form of positional crowd control, they are not loss of control. Roots, however, show up on the loss of control frame, and so might trigger the damage mitigation.