Who knows if it is an imbalance though? Presumably there is a reason why one have a 22 sec cd and another have 15 sec. Otherwise, give them the same cd.
Does it really matter what you call them though? The moment you add a legendary consumable to a rare, it is technically no longer a rare item but something new. A legendary with random affixes. You can still have rares alongside those two other item types (fixed legendaries, random “rare-legendaries”, and random rares,all with their own value in end-game).
Yeah, that is certainly a skill modification system as well.