Crowd Control effects are for crowds, not for single enemies.
If an encounter is designed around a single enemy and that enemy isn't immune to CC, then at best it just means the fight is trivialized, and at worst it means you spend the entire encounter chasing after an enemy being bounced around by your own [parties] attacks.
Bosses and mini-bosses being affected by Crowd Control is purely a negative for the game, and leaving all pre-2.1(?) bosses with no CCI is hurting the enjoyability of those fights significantly.
Please just go through and give them all CCI.