Well I think you're entitled to point out unrealistic things if you want, and as Tav says you've nailed one. And in the same vein:

Lulu is a guardian with 2 pilgrimages under her belt(s), yet she only has Level one Elemental magic after getting all the way to the Calm Lands (twice).

Even worse, Auron is a "legendary" guardian with just Power Break and average stats.

Of course the reason is game balance. Otherwise Auron/Lulu/Yuna could walk the whole adventure on their own.