I've figured out why Schaffrillas can't stand The Bad Guys.
James is a purist when it comes to animation. He views live-action films as "adult" and he views animation as "for kids, but allowed to be dark and have some adult themes."
The Bad Guys is a child-friendly version of an adult live-action film. It's the DNA they took from the books, which were send-ups of R-rated films Aaron Blabey watched as a child. You can tell by the kinds of camera angles and shots, the lens effects they get from mimicking life-action cameras, the romantic/sexual tension between Wolf and Diane, even the way the dialog is structured. All of it screams that it's intended for adults, between jokes about a piranha farting.
It goes against everything be believes, and he literally cannot process what he's watching. That's why he's so stingy about saying anything concrete about either movie.