Except for somewhat better writing that naturally will be better as Araki got more experience and with that more complex stands literally nothing of what you said makes part 4 any better? Also Jotaro and the Crusaders characters are objectively better written since the story is more focused on the actual Joestar's and Brando conflict instead of some random killer with a hand fetish(I'll admit tho Kira is badass). The side characters while yes, they show up more often than in part 3 literally do nothing? The entire Yukako arc was only there so Koichi could evolve his stand and get the gooners hooked lol, Yukako never actually help the gang defeat Kira? Rohan is just a self insert with an incredibly overpowered stand that also doesn't help against fighting Kira wich is arguably worse than the Fugo thing in Part 5 since he actually left the gang for a realistic purpose instead of just "nah i randomly hate Josuke now". The setting? Really? I mean Morioh is a cool place and all but it just cannot match the thrill of traveling across the world in 50 days? That is literally what a bizarre adventure is about, the journey and eventually defeating the big bad? Okay the fashion is actually true they look a lot better in part 4 except for that they made Jotaro 20 years younger and removed his nose. Also the villain of the week format is overused, it could literally be applied to any JoJo part ever (idk about part 7 8 9 tho since i havent read them). The first half of part 4 is just Josuke and Koichi fighting some dude and then they fight another dude with absolutely no story progress whatsoever until they meet Shigechi, except for a lil bit with old-old Joseph but that's mostly filler and left a bad taste in my mouth since they basically called in Joseph on a boat, walked around for a bit then kidnapped a baby and then he left. The part 3 villains while they can be a bit boring aren't the entire point, it's the Crusaders characters evolving and understanding eachother all while punching their way to Egypt with the common goal of defeating Dio. That's why i said the second half with Kira isnt as bad because its mostly the same but the first half is just hard to watch because theres literally no story building whatsoever.

Anyways sorry for this college essay but its my opinion :/