So true. This season was the first season I actually fully realized (and I know on the surface this sounds ridiculous) that Mr. PeanutButter is a dog.
Meaning that he has the urge to be unconditionally loving always and is easily distracted and excitable, but also has this deep-seated fear of abandonment because of his divorces. Of course his ex-wives are crazy and abusive, and of course he hasn't necessarily learned from that and changed because he is flawed, like the other characters, like a human - like an emotional being, capable of rationality and compartmentalization. Dogs want to please humans; PB is a bit of a pushover, people-pleaser, [and Diane is a bit of that as well because of an emotionally traumatic upbringing, which is probably why she lost herself in him, and only when she started to form her own identity and disagree with the person she was closest to in her life did she realize how goddamn miserable she was. She started to respect herself, take a wider berth away from old patterns and habits learned in childhood and realize this unconditional love wasn't enough or what she needed as an adult].
Princess Carolyn, BoJack and the other anthropomorphized characters have these kind of subqualities of animal behavior - like PC bathing herself or always landing on her feet (literally) and BoJack doing that horse 'brrph' thing, you know what I'm talking about - but they are ultimately more humanized than not. Yet PB seems not to be, he's more like a dog given qualities of a human and not the other way around like the other main animal characters seem to me.
What felt like a flop character at the beginning has taken on a whole new meaning and weight in the show for me. Might've been an oversight/lack of open-mindedness when past-me watched the 1st season, which along with the 4th is the only one I've not rewatched, but...
I'm excited to see what they do with PB/rewatch what they did, because he's set up in such a way where this character that is based on an animal that has specific human-perceived traits in the real world is translated kind of perfectly in this alternate reality and I definitely have a new appreciation for that creative choice.