Shadow priests baseed on their mythic dungeons performance?
Because in raid they're by far the strongest caster and overall dps too on certain fights, doing up to a 100k more than an average dps on bosses like dragons of nightmare. So idno wtf you're talking about
It wouldn't make sense to buff frost dks when they already have unholy being pretty fucking good. Same thing for the frost mages, fire is top 2 caster and doesn't really have any flaws unlike most specs(shadow is stronger but has flaws for example) and it wouldn't make sense to get arcane on the same level/better for certain fights.