Let's acknowledge Vergo had the advantage of having Law's heart. Still, the feats he displayed against Law and Smoker were pretty solid:
- Outpaced Law's teleportation as he tried to grab his heart back via shambles.
- Took Law's Counter Shock without flinching.
- Brutalized Law with his hardened punches (and earlier with his hardened Bamboo) harder than Big Mom did with her hardened punches (as @ZenZu pointed out though, Big Mom has more in her arsenal). Even if you argue Law's endurance grew, 1) the increase won't be so exponential to explain his jump from being brutalized by a mere vet to tanking a Yonko's repeated punches, especially since he 2) was already heavily injured and vatigued
- Overpowered and brutalized Smoker. Same one who pressurized Law in the first place.
Then, we have the Sanji incident, where Vergo cracked Sanji's leg with a basic, unhardened kick, when legs are Sanji's one and only weapon, his bread and butter, his speciality. That is, after comfortably eating Sanji's Diable Jambes and having Sanji comment on Vergo's toughness like being that of a mass of iron and admitting it would've ended bad against Vergo if they continued.
And we haven't even witnessed Vergo's all out style - full body hardening with his Bamboo. The only time he used the FBH apart from the flashback with Rosinante, was when he charged straight into Law's mountain slasher hax, believing he doesn't need to dodge due to being that confident in his Haki.
Yes, FBH Bamboo Vergo will defeat Jack.