Jack is really overrated. He has a bounty near that of katakuri despite being a YC3 and he was able to fight on par with Inuarashi in his full zoan form. He literally didn't even need hybrid to take on Inuarashi and Inuarashi is probably on par with a yonko veteran.
People sleep on the YCs because Luffy beat two of them when in reality, they are stronger than most superrnova.
Also, there won't be nearly enough time for a drawn out battle between Who's Who and Jack.