tbf Mighty Guard isn't useless (though Mix is better, but Mix is the single best ability in the entire game) and I've got some mileage out of Stone Breath and Bad Breath, but yeah, he definitely suffers and a jack-of-all-trades just doesn't really fit into how FFX does things.

However, Zell was the joint-best part of VIII and one of the best characters in the entire series, both in and out of combat.