Lets compare frost, the current TRASHIEST dps spec, with fire, the MUST HAVE spec for raid/m+: both have a really cool CD (Icy Veins, Combustion). I don’t think they should nerf fire, but the other 2 specs should be at least viable dps-wise.
When SL launched you could still see a bunch of Arcane and Frost mages… After Castle Nathria was out, most mages just went fire and arcane/frost are rare sightings.