From what I know of Groth he's an incredibly opinionated SOB but far from humorless. He's quite smart, intellectually challenging and possessed by a wonderfully funny dark streak, but it's also true that he's fairly arrogant.

I enjoy reading his arguments with other people, but I didn't find his opinions on (what I consider to be) minor comic book creators holding my interest or my agreement, so I stopped my TCJ subscription almost a decade ago. So while it's not unfair to consider him an asshole, my sense is that it's inaccurate to describe him as a humorless asshole.