Why not just strip all mobs of mez protections, and simply give them % of mez resistance. So if you hit a boss with a minion level hold, it does hold the boss, but only for like 1/10 of a second or whatever, but hit him with a boss level hold and he would be held the entire duration. I mean, we already have mez resistance in the game, and we already have resistances scaling with level. Seems like a straight forward solution to me.