As seen in the Invasion, he can actually be pretty competent. But appearently only if he's really pressured.
Well you need training to be good at using any close combat weapon.
He just doesn't have that
Being a Shooter
He's learning. And he's okish.
Thinking on the fly
Agreed he needs more experience for this though as well.
Inba he's a genius
He's the most below mediocre guy ever. Slightly good at tactics but that's about it.