I disagree, Part 4 had a pretty great even fight between Josuke and Kira and the way it ended unexpectedly was a nice change of pace from how normal Shonen final battles go, and at least there was some implication for why Jotaro had similar powers to Dio even as far back as when we see Dio use a Purple Hermit kind of Stand along with Dio merging with Jonathan's body to make sense. The big problem with the "ultimate Hamon" was how Joseph literally had no clue about it and just so happen to be in the perfect spot to use it even after giving up and than shit like his sliced off arm just so happen to catch Kars before he could kill him. The sheer amount of coincidences was almost too much, but Joseph purposely lying about planing it all even though he admits to himself it all was just luck all so he can spite Kars was funny as hell.