You're asking a questiong without a definite answer. It's technically fictional and open to interpretation. I don't even know enough about Terra to form a complete opinion. My bias puts her besting her group in a fight.

The last technical answer is all based on game mechanics. To have my own perhaps unique and dull that he wasn't half esper or special in some sense. But why should that matter when a competent character can contribute. Regardless of their background/scene appearance.

Because we can't draw a definite conclusion someone can keep objecting/sustaining.

His personality is dull but he's good with gunblade. Maybe a little of both good and bad. If that's the case why debate it?