The only suggestion I’d add to T&E’s idea is this.
I would allow these options to be open to more than just specific races. That was actually the big reason I suggested a second T-Mog tab exclusively for spells in my post on it. This would allow players to customize their character.
See I totally dig his Vindicator Priest idea, but I am also aware my view is only 1 of a million. There might very well be someone that likes being a Lightforged Shadow Priest (Even though I agree with T&E that such a combo makes 0 sense by the lore).
So how do we add these much needed customizations, without taking options away from others? Well, it seems to me like the best way to fix such lore discrepancies, is to just have the options on the table for everyone like City of Heroes did with Spells / Abilities.
Maybe you run around in a Clown-Suit shooting sparks, or maybe your a grim crusader. But in all cases, the player chose their design concept as the avatar is ‘their’ hero.