What the hell is the point of having exponential damage reduction to certains types of magic if the abilities/auras/totems don't stack right? Please change this terrible mechanic.
Are you talking purely about resistance abilities like fire resistance aura / totem, etc?
They're hold over from wow. Those abilities stack with item resistance but not each other for the purpose of providing various sources for these utilities that are needed for certain fights for various comps that you may run.
Though the comps thing isn't as necessary since we're all classless now.
Should still stack even if they're a similar ability in my opinion, but if this was the case then Bountiful Gift RE should be unaffected and actually stack right with other abilities but it doesn't. So you could have say Aspect of the Wild on and use Bountiful Gift but it won't actually work right together when it should give you 150+ resistance in nature before any item resistances.