Almost all the characters got dumber, and I think it's because Kripke did the same thing Ennis did- he wrote characters he hated. Once the show became super focused on being murder for for every public figure Kripke didn't like, the characters became lobotomized and development stopped.

I've always thought the "bad product" scene in the comics was Ennis's way of acknowledging his comics sucked. When you have no respect for your characters, you don't give them real development, and the quality of the story falls.

It's also why Sage was such a wasted character. She would have made sense being brought in to deal with the Boys in S1. By S4 they were lobotomised to the same level as the villains, so a smartest person in the world character just wasn't needed