The Deep is interesting, because it’s rare to see a character not only reject a redemption arc, but decide to become an even worse person.

In season 1 it's clearly he's a douchebag rapist, but not as much of a psychopath as Homelander is (low bar I know). His only redeeming quality being that he seemed to genuinely care about sea creatures. In season 2 when he talks to his gills (while drugged), we get to see how his inner psyche works. Deep believed he needs to humiliate others first because they'll mock him for being mutant supe, and this is shown to be true to an extent. A-train put a blowup dolphin with lipstick on it's blowhole in Deep's bed as a prank, Homelander says his gills are disgusting, and even at the tower Starlight says he's known as "the fish guy". There was some setup to get you to sympathize with him. However, because he never gave himself time to self reflect, by season 4 Deep just disregards all lessons learned. He decides to vent out his anger on innocent people, and even says he'd kill every fish in the ocean for Homelander. It's a nice contrast to me that as A-Train got better, Deep would become worse.