Technically he's not. He's put there but that's due to his personality and not strength. This is the same chopper who fought an opponent stronger than Franky back an enies Lobby and immensely destroyed his opponent with monster point.
My pitch was that Chopper finally gets a new form/forms able that makes people take him seriously. Depends on what Chopperjiji actually leads to. Tbh, while I like Killer, he's a secondary character who is currently dealing with Hawkins. Not to mention, now every single fight is Strawhat centric.
Though, maybe Jack comes to the performance floor or something, and Luffy has Yamato leave the roof by jumping down through the hole in the roof back to the performance floor, so she could still fight him as well.
All just possible options, but I disagree about Chopper being weak.
I think chopper will fight the number whos devil fruit was successful.
hawkins is just a stalling fight for killer the same for inurashi and jack.
Realistically no straw hat can fight jack or has a reasonable power up that makes it make sense.
My reasons for killer vs jack are
Jack was introduced in the same chapter Killer was in back in punk hazard
both have an iron mask
same weapons
same type of hair
jack is a more defensive fighter while killer is more offensive
The structure of the fight.
Killer fights two yonko/fights hawkinsthen fights jack
jack fights army/then fights inurashi/then fights killer
also I realized that both hawkins and inurashi have a personal connection to both fighters. Killers alliance with hawkins before wano and jack messing up zou