Runic, (Can I have it?)

[Raksha]

On a concept level, magitek knights (which is basically what Tina/Terra and Celes are) are rather close to Red Mages.

The reason Paladins have cover is because of cecil who made it a staple ability for PLDs in FFIV. Runic and Cover have nothing to do with one another. That's not even going into how one belongs to a knight and the other belongs to a magic swordsman. PLD is of the former, RDM is of the latter (refresh-whoring notwithstanding).

Justify it however you like. Cover is a PLD ability because that's what tanks do. Magic cover would be the same way.

Not that some random wiki is a reliable source, but:
http://finalfantasy.wikia.com/wiki/Celes_Chere

Celes's abilities are similar to Terra's. She has all-around high stats and equips swords, maces, some daggers, heavy armor, some hats and robes, and all shields. She also has access to female-specific equipment. Celes and Terra have almost identical equipment draws, except for the Cotton Robe, and their respective ultimate weapons in the Advance release - while Terra uses the Apocalypse, Celes wields the Save the Queen. Celes's ability is Runic, which negates the next magical ability used and heals Celes of an amount of MP equal to that ability's MP cost. As she is rescued from prison when she joins the party, Celes joins wearing only a Hair Band.

Along with Terra, Celes is the second party member to be able to learn magic without equipping Magicite. Compared to Terra, Celes' spells are more defensive in nature,and she learns more status spells while Terra learns more damaging spells. She also learns Ice element spells, contrasting with Terra's fire spells.

Anyway, i'm not gonna argue ff6 with you. The version of runic presented in the op is more PLDs flavor. Not saying that it's a bad idea or that RDM shouldn't get it or anything like that, i'm just being pragmatic. If SE implemented as in the OP it would be a PLD ability.