Inuarashi is not currently fighting Jack for revenge, but so that he doesn't create more victims. Inuarashi also told Nekomamushi to leave Jack to him.
Besides, Inuarashi could be stronger; he's one of the four that performed Togen Totsuka after all.
Yamato and Law are needed much more at the Yonkou fights than they are needed vs Jack. Jack is not a threat to the broader war effort currently. His only intention is to deal with the Minks and Raizo. Even if he defeats Inuarashi and is freed, he's far from a priority.
Linlin is a loose Cannon and virtually a natural disaster. She's regained a three of her homies, and Law has expressed his desire to engage her.
Bao Huang declared that Kaido is heading below the Rooftop to oversee clean up:
He's already taken out Kinemon and is heading for Momonosuke. He needs to be stopped, and Yamato is the only unoccupied that's strong enough to do so (if you assume that Law makes it to Linlin).
Yamato also needs to fight Kaido.
Your argument for Law/Yamato dealing with Jack seems to rest on two premises I find dubious:
- That Jack will defeat Inuarashi.
- Inuarashi may yet win, but even if he doesn't, he can probably hold off Jack for a while before he goes down.
- That after Jack defeats Inuarashi, he'll need to be stopped.
- Compared to Kaido and Linlin, Jack doesn't even register as a threat.
- Furthermore, Jack has displayed no indication to interfere with the core objectives of the alliance (protecting Momonosuke, defeating the Yonkou) and only seems to be acting out of some personal vendetta against the Dukes and Raizou.
Tl;Dr: it's the Yonkou not Jack that needs to be stopped.