because he never wanted her to join?
Yes and replace that fishman/kappa guy with Yamato.
Have Kawamatsu actually protect Hiyori, rather than be a whining bumbler when it mattered most.
Have Denjiro operate against Orochi, but command enough strength in the Yakuza district that Kaido respects Kyoshiro over Orochi, creating tension.
Like you said, put Yamato where Kawamatsu was. BAM. Actually sensible plot. The princess of Wano running away from one Scabbard to be magically found by another is so dumb. So much of Wano is reductive. All of this hype for Kawamatsu, the guy in the cell, and he's imprisoned because he was so useless, he couldn't find enough food to feed him and a toddler... when we all know he can survive off of eating poision fish. MAKE IT MAKE SENSE. HOW IS HE STARVING WITH HIYORI, IF HE CAN SURVIVE FOR OVER A DECADE ON SMALL AMOUNTS OF POISON FISH???!?!?!?!?!?!!?!?!!!!??!?!?!?!?!?!?!?!?!?!?
HOW THE FUCK DOES THAT MAKE SENSE ODA?!??!?!!?!?!?!?!?
Kawamatsu cared so much about Hiyori, that he left her alone in the wilderness so she could run off.
Once editors became too afraid to challenge Oda this series became riddled with plot holes.
So much shit in Wano was "OOOOOOOOhhhhhhhhhhhhhh the Witching Hour Boy, who is he???" and we have like 50 panels teasing this shit, and the reveal is, "Oh yeah it was Kyoshiro/Denjiro the whole time".
Wano in terms of creativity is a 10/10 arc, in terms of execution it's a 6 or 7, and IT'S SO FRUSTRATING