That's a job issue rather than an armor issue. The armor is great. The job? Could use tweaks. Lots of them. Immunity is the worst part of it all, really.

The biggest issue with just giving monsters extremely high magic evasion is the fact that Accuracy (both physical and magical) floors at 20%. Even a Mnk/Whm could land Silence on Suzaka at 75 in 2005~, they just have a 20% land rate. Even if they gave a monster +1000 MEva, even a Brd could land enfeebles if they spammed them enough. Beyond that, the actual difference between RDM enfeebling and WHM or SCH enfeebling has dropped dramatically over the past 2 years. Red Mage would need something to actually set it apart from the crowd in the Enfeebling department in order for it to become relevant.