Luffy has been shown time and time again throughout the series to take inspiration from other people he encounters, obviously most recently with Katakuri’s future sight.
He took Red Hawk from Ace, Soru from the six powers (Which I honestly feel have been a bit underused in the series, imagine Sanji with wind kick one, but) some people think Gear 4 is inspired by Bellamy, I’m sure there are more examples. Anyway this is an established thing by now.
Here comes Urouge, every time he gets hit, he somehow hits his enemy back harder. Urouge ate a Devil Fruit that allows him to convert some damage inflicted onto him into strength, which results in expanding muscles and body size.
This would be something that would really resonate with Luffy I think, he’d witness this and realize he can do the same thing. Using his rubber powers he’d absorb the force from the blow, transfer it through his body and out the other side. Like when you throw a rubber ball at a wall and it bounces right back at almost the full force you threw it with. If Kaido is the strongest 1 on 1 fighter in the world, it stands to reason that the only one that can beat him is himself. If Luffy can absorb the force of the blow and return it to the sender on top of the force of his own punch, he could beat any other physical based fighter in the world. The cool thing about this is that it’s been a staple of his since the beginning, except with bullets instead of punches. When he gets shot he just sends it right back. It would feel like coming full circle.
Like I said though, this doesn’t make him an unbeatable god, which is why it’s perfect imo. I’ve seen people saying stuff like “If Luffy can beat Kaido straight up 1v1 might as well just end the series because he’s the strongest now, it’s boring”. But this doesn’t work with swords, doesn’t work with fire, lava, ice, light, etc…
It would cement him as the best fisticuffs fighter in the world and give him an insurmountable advantage in hand to hand combat, but the fight with Blackbeard or Big Mom will still be climactic because they can use their abilities in interesting ways to circumvent it.
*Theory by Gravelord-_Nito