Basically the way I see it

they start the game even, but then they develop differently throughout the game. Because of the way they developed, Squall ends up better than Seifer in tactics, strategy, and leadership. Seifer ends up stronger in pure strength. The simple fact is, if they switched places, and experienced what the other did, they'd be reversed.

Take two dogs, treat one nice all the time, and train it. Versus taking the other one and beating it all the time. One will be a people person, and "think" more and have more talents. The other will be brutal and strong. That's basically how these two were.

THE JACKEL