It’s pretty much been laid out in the show that he’s a bad “therapist”, mainly because he’s not an actual therapist, just a horse therapist. So I always get weirded out when people try to utilize what he talks about to analyze Bojack as a character. I thought the conversation about him drunkenly telling Bojack that he has a secret hatred for horses was meant to be a joke about how much of a hack he is, since it’s such a baseless assumption that it’s even proven wrong later in the series (when he visits the horse historical village place). He’s meant to satirize “therapists” who don’t have any more qualifications than an armchair, right?
Either way, I love it when shows do make therapy a flawed process. We did see an actually good therapist later in the series, and even then she slipped up now and then, and I felt Dr. Champ was supposed to be the antithesis to her. It makes the show feel even more grounded in reality, than therapists in other shows basically being the talking piece for the writers to roast their own character.
I don’t think it’s objectively wrong to read Dr. Champ as correct, but it feels kind of thematically hollow and not like something the writers would do, for a couple reasons:
Bojack’s issues mostly already have mundane, realistic explanations behind them, it just seems unnecessary and out of left field to add another explanation that doesn’t have much of a connection to the other, adequate reasons that have already been given. There is no horse who Bojack hates, where that hatred doesn’t already have a better explanation of some kind.
I don’t think it makes a compelling plot point. Bojack’s problems are all real things that exist, but the viewer has no context for what it means to “be a horse” and to feel guilt about that. As an emotional beat, it’s much easier to connect with his anger towards his parents as people as opposed to a hatred of horses. I mean, you could stretch it to be some sort of allegory for race/ethnicity, but six seasons in it just feels like a contrivance that wouldn’t add a whole lot to the story.
The viewpoint of the show is generally that self improvement is the result of work, not one-off epiphanies, especially ones that happen while drunk. It just seems a lot more likely that an “aha! this explains all my problems!” moment would be satirized rather than played straight.
Bojack idolized Secretariat all his life, that’s another counterexample besides Hollyhock. And, I don’t think Champ’s argument against Hollyhock as a counterexample actually makes sense. I think it’s true that Bojack sees Hollyhock as himself, but he clearly loves her. He hates himself for what he feels he’s become, not because he’s a horse, and he wants Hollyhock to go down a different path.
Bojack not knowing a lot of horses just kinda makes sense. There are all sorts of different animals in the world, not that many of them are horses, and Bojack doesn’t have that many close friends. It would also be strange to write additional characters in that are the same species as the main character without some reason behind it (e.g. his family members, Secretariat, and Champ). Like how two random characters in a show will almost never have the same first name unless there’s some reason for it, because even though that’s a thing that could just happen by coincidence in real life, it sticks out to the viewer of a TV show.
All that said, I do still think it’s open to interpretation, it’s totally possible there’s something I’m just not seeing here.