How to improve Jack, Inu and Neko's plot significantly:
-Put kid Jack in the middle of the battle as the Scabbards scape execution because he was taken by the crew and wants to impress Kaido (since he always puts himself in danger for his group).
-Have some danger threaten him as he tries to stop the Scabbards.
-Inuarashi wants to save him because he's just a kid, Neko doesn't because it's more important to leave alive for Oden than a kid; this is where their feud starts.
-Jack is saved only to become their worst nightmare years later. Oda builds a narrative on loyalty (being loyal to the Kozuki clan versus to the Beast Pirates who gave you a home) and how dawn will only come for one of the two that night.
-Have Inuarashi and Nekomamushi fight and defeat Jack together in a real versus where they work together as they used to, as it should have always been.
And that's how you get something a big more interesting than whatever this was, which wasted both Jack (who deserved a proper fight) and Perospero (who could have worked way better with more tricky subplots regarding the alliance, Marco, etc.).