Zatsuyou Fuyo Jutsushi ga Jibun no Saikyou ni Kizuku made - Vol. 2 Ch. 8

[GuildMasterJin]

My hypothesis about the discrepency that exists between the perception of Wim's skills and competency arises from the combination of [imcompatibility and actions of his previous party (Dragon's Wing) members] with [Wim's habits and social anxiety]. Due to DW's combat exclusion/isolation (that arose from an ill preconceived belief that he's incompentant judging solely from inadequate people skills) his level was forcibly capped by his party. During his time inside the Dragon's Wing party, he honed and refined his Grantor enhancements skill through dedication to his studies while keeping up with daily fitness training. Once he was able to solo defeat the boss by a chance situation, Wim became able to replenish/fulfill the imbalance of skills and experience.

This is what I assume is causing the perceived discrepencies based on the information that was provided up till now from the previous chapters, I could be wrong tho