No, his cheerful disposition [Forced though it is at times] is definitely a nice contrast with my own somewhat serious nature.

[They all share a bond with Noctis, and that is what has drawn them together as a group, but it's their own efforts that have made them a cohesive unit.]

What Prompto suffers from is a crippling low opinion of himself. If he had more confidence, he could "keep up" with the rest of us. He still feels as if he has to earn his place among our group, but he is the only that feels that way.