Chopper actually fights in hybrids forms most of the time, and in fact his basic hybrid/Brain Point was first introduced as very important in battle, but he's quite a non-representative example because of being a reindeer with a human fruit instead of a human with whatever animal power and having tons of modified hybrids.
Edit; Didn't Jack literally battle to the KO with just his Full Zoan form?
He also went base as soon as Nekomamushi tossed him in Zou and seemingly stayed like that against a whole army considering Wanda's memories on the battle. And I'd say that he only fought the sulong minks in animal form because Oda wants to save his hybrid for his ultimate versus in Wano and not some in-verse power logic.
Edit: Consistent framework, different abilities have different trade offs and different forms take advantage of that.
The problem is that like 90% of the time, when the fight was actually definitive or simply serious and demanding, zoan user went hybrid. This has happened in literally every final versus with an enemy (Boa sisters, Lucci, Jabra, Kaku, Funkfreed, Miss Merry Christmas) and in most of the cases (if not all of them) that a good guy faced a rival that required his full strength (Marco, Chaka, Pell, Bian, Kabu, Dalton... even Chopper has never defeated a strong adversary without resorting to one of his rumble hybrids, if I recall correctly).
Kaido just went back to human ready to end things with the scabbards, just like he defeated Luffy and Oden after doing next to nothing as a dragon. And odds are that most if not all of the Beasts Pirates will turn hybrid to handle their final versus. Yeah, Ulti went full beast against Luffy, but Page One went hybrid against Sanji; Jack was defeated in mammoth form, but soon went human in Zou; and even tertiary characters like Epoida, Dalmatian or Onigumo mainly relied on their hybrids when they fought in Marineford. Against all of these examples you can only bring one or two people like Pekoms and Chopper and characters who didn't have their actual, serious match yet (like the Beasts Pirates).
Of course we can say that some abilities have their own strengths in full animal, but Oda has been pretty consistent on portraying hybrid form as the strongest as a whole. In all case, the other two may have (not all of them, which makes it really hard to establish a rule) situational strengths for particular contexts, but that's pretty much it while hybrid is consistently the most reliable bar Chopper, who on the other hand took advantage of science to create artificial hybrids that are far above his animal form.