I agree the levels don't come up very often and can feel at odds with the story at times. However, in this case it's "he's both real fuckin' big and high level", so it's not really an example.You know, it was kind of inevitable that eventually we wound up in a brute force vs. skill type match... but in a setting with levels, it's strange to have the setup be "he's just real fuckin' big" as the reason.
TBH levels and other such gamified elements are just a detriment to an otherwise grounded series anyways and shouldn't have been introduced to begin with.
Yajin would have no trouble with a level 1 person who is the same size.