It makes more sense, at the very least.
In making these games linked, (FFXII + Revenant wings, FFTA + FFTA2, and one other that i forget at the moment) I believe the developers wanted to have different aspects of the games merge into one another. Hence we have the FFTA races in FFXII, the bazaar system from FFXII into this game, and other things as well.

Back to my point, white magic as we all know is about restorative magic, be that healing or reviving. While protect and shell kinda fit in that category, they fit better in the green magic of buffing and protecting your guys while debuffing the enemy.