Leech immune would be really tough on Rogues. We're pretty squishy without it.

A current example similar to leech immune - champion mobs with the Tough/Phased combination. While the barrier buff is up, I don't leech enough keep up with the incoming damage so I have to chain stun until the buff drops. With leech immune any sort of damage resistance, damage shield, blind, juggernaut, or normal hard hitting mob would probably kill me.