I do think it is silly that geo-debuffs are irresistible when noone else's are, but lets be frank: the debuffs GEO are generally using are stronger than what anyone else even has. (Frailty is much stronger than Dia III, with upkeep being much easier, Vex and Malaise are in classes all their own) I've never seen anyone ask a geo for slow or paralyze. It's nice when "Hey, Meteor got paralyzed" but it's nicer when the raid knows they're going to take minimal damage from it because of Vex.

I don't know if they can make using these debuffs desirable again, but I do know that the spells (Paralyze, Slow, Blind, Addle) already have the mechanics in place within their calculation to make having a well-geared RDM preferential to someone's refresh mule.

Maybe RDM needs a trait that makes their spells unresistable. 5 years ago, it would be ludicrous to say that, but GEO got it.