It's true, but Red Mages make up for their weaker magic by being able to dual cast their magic, so it's just as strong, if not stronger than a Black Mage's single more powerful spell~ And being able to equip a decent amount of armor allows the Red Mage to tank a few hits without having to worry on focusing on healing, and with their ability to wield actual weapons, they can fight against enemies when the Red Mage runs out of MP or is Silenced. That's the thing about being a Jack of All Trades, you can do it all, even if you're only decent at it~
[s]And of course, if you're like me, who's a Red Mage that has a subclass of Red Mage, you can dual cast your dual cast, thus getting four spells off in a single turn, definitely doing more damage than a Black Mage~[/s]
I see you're point... Of course, I never meant to say that the Red Mage is bad, just that I don't prefer him nor see why others do, but that makes sense. Though, I don't recall dual casting being in the first few Final Fantasies...