I was absolutely your opinion with jack before. But had some discussions here and they kinda convinced me.
You need to keep in mind that Jack is still pretty young. Way to young to get be too bound somewhere. For me it seems like the beast pirates, beside of Kaido, King and Queen, are mainly structured just through power. Nothing else. No real connection, no boundaries of "real loyality", its all about strength. Thats the way to get higher in position, thats the way to survive.
And if that big main force, i.e. Kaido, isnt there anymore, the whole construct will fall completely. Means maybe Queen and King will stick with Kaido, but beside of them, the rest is just connected to him through his force. And if someone comes up with more strength, or at least way more potential, i.e. Luffy and Kid, in their understanding it is absolutely natural to change their loyality to them. Thats just the system Kaido build there. You could see this pretty well through the fact the Tobiroppo aimed for the heads of King etc., just to raise up. There was not a glimpse of loyality.
Additionaly i can see Heat and Wire taking over the fight against Jack when Inu is about to lose. So they could absolutely just take him hostage first, because we already know he regenerates pretty fast.