I'm pretty sure MACC will still help, just like it helps a RDM land enfeebling magic or dark magic like stun... I am pretty sure Dasva's right this will be a big boon for BLUs
And yes, you will have to make gear choices. Obviously if 20 MACC is more potent than 5 BLU skill (or whatever) - then equip the MACC... I am not sure what the issue is here.