That's some decent headcanon. Red Mage is also just a very good and versatile class so it's definitely a very solid and popular choice.
I really only care about seeing big numbers though. If I don't annihilate my enemies then Im not interested. Don't know what that says about me but that's just how it is. I also like that many of the higher level Black Mage spells actually look and feel powerful. Something that not every game gets right.