There are 5 candidates imo who have at least a small iota of a chance of being the one to beat Jack imo: Luffy, Yamato, Jinbe, Inuarashi, and Usopp
Luffy: He did mention in Zou how he wants to beat both Kaido and Jack, and having Luffy come back and one shot Jack could be a good way for Oda to show us how strong Luffy is going into the final round vs Kaido. However, I don’t see why or how Luffy would end up on the 2nd floor, and Luffy trashing Jack would be lame since it deprives someone else of a good, fleshed-out fight with Jack
Yamato: If for whatever reason, she decides to leave Kaido to Luffy alone or Luffy tells her to leave Kaido to her, then maybe she could run into Jack and beat him.
Usopp: Unless P1 gets back up, Usopp doesn’t have anyone else to fight except maybe a few Numbers (which I think Chopper would be more likely to fight than Usopp would be). Oda could have Usopp beat somehow (it would obviously be in a rather outlandish manner than a straightforward victory) in order to set him up as Luffy’s “YC3”, which would make sense since he should be surpassing Yasopp, one of Shanks’ YCs, and he was among the trio that fought Arlong’s officers. Usopp would need to have an explosive growth in strength, so maybe Oda has him fight a weakened Jack and get a lot stronger via a powerup so that Usopp can beat Jack with a good strategy.
Jinbe: Jinbe beat WsW pretty easily and clearly has a lot more fight left in him, so a somewhat weakened Jinbe could fight a weakened Jack. Jinbe should be around Jack’s level, given how he beat WsW mid diff (though I do think WsW could maybe get up later and fight someone else).
Inuarashi: I honestly think that Inu has a 0% chance at beating Jack, unless Neko somehow shows up to help him. I would be here all night if I tried to list all the reasons why I think Inu beating Jack solo is impossible, so I’ll just leave it at this: Inu is far too irrelevant in this arc to justify getting the glory of beating a Calamity, and he’s clearly not as strong as Jack when he doesn’t have access to Sulong. If Inu was a main character in Wano like Kyros was a main character in Dressrosa, then I could see Inu being the one to beat Jack for narrative reasons, but Inu got basically no screentime in the first two acts, and all of his fairly limited screentime in Act 3 was shared with 8 other people. He’s just not important
I think Jinbe is the most likely candidate, then Luffy, then Usopp, then Yamato, and then Inu at last place
Luffy: He did mention in Zou how he wants to beat both Kaido and Jack, and having Luffy come back and one shot Jack could be a good way for Oda to show us how strong Luffy is going into the final round vs Kaido. However, I don’t see why or how Luffy would end up on the 2nd floor, and Luffy trashing Jack would be lame since it deprives someone else of a good, fleshed-out fight with Jack
Yamato: If for whatever reason, she decides to leave Kaido to Luffy alone or Luffy tells her to leave Kaido to her, then maybe she could run into Jack and beat him.
Usopp: Unless P1 gets back up, Usopp doesn’t have anyone else to fight except maybe a few Numbers (which I think Chopper would be more likely to fight than Usopp would be). Oda could have Usopp beat somehow (it would obviously be in a rather outlandish manner than a straightforward victory) in order to set him up as Luffy’s “YC3”, which would make sense since he should be surpassing Yasopp, one of Shanks’ YCs, and he was among the trio that fought Arlong’s officers. Usopp would need to have an explosive growth in strength, so maybe Oda has him fight a weakened Jack and get a lot stronger via a powerup so that Usopp can beat Jack with a good strategy.
Jinbe: Jinbe beat WsW pretty easily and clearly has a lot more fight left in him, so a somewhat weakened Jinbe could fight a weakened Jack. Jinbe should be around Jack’s level, given how he beat WsW mid diff (though I do think WsW could maybe get up later and fight someone else).
Inuarashi: I honestly think that Inu has a 0% chance at beating Jack, unless Neko somehow shows up to help him. I would be here all night if I tried to list all the reasons why I think Inu beating Jack solo is impossible, so I’ll just leave it at this: Inu is far too irrelevant in this arc to justify getting the glory of beating a Calamity, and he’s clearly not as strong as Jack when he doesn’t have access to Sulong. If Inu was a main character in Wano like Kyros was a main character in Dressrosa, then I could see Inu being the one to beat Jack for narrative reasons, but Inu got basically no screentime in the first two acts, and all of his fairly limited screentime in Act 3 was shared with 8 other people. He’s just not important
I think Jinbe is the most likely candidate, then Luffy, then Usopp, then Yamato, and then Inu at last place