My theory is that in addition to McCracken’s design work on Dexter’s Lab and PPG, the admitted influence from Drawn Together/South Park, and Invader Zim, the Gainax Guys took some inspiration from Bleedman’s webcomics from the early-to-mid 00s. They were significant enough at the time to get Cartoon Network’s attention, and they bear a striking resemblance to aspects of PSG’s aesthetic. Pic related is from 2004.