Oh, Logan's not a skeptic, he's a secret fan. At least of his enchanter skills.
The protagonist has always been a prodigy, but he's a prodigy at being able to excel at many things (not master it). So I think it follows that not everybody can be as excellently well-rounded as he is, though it's natural that he'll be outdone by specialists.
There's no weak-to-strong element for him, it seems he was always talented and strong in general, just overshadowed by being around with specialists in the hero party who are masters of their specific fields. So he's a jack of all trades, but I don't find anything wrong with that. Being well-rounded and versatile can be amazing.
I guess he's only resentful of it because he personally desires to specialize with the sword? That aspiration though. So he wants to be a one-man party. Another lone wolf black-haired solo swordsman...