Pretty sure the 100 times stronger thing is just a raw estimate. I doubt all the SHs had the exact same growth rate and Rayleigh has always been a top tier who had a decline in strength and stamina with the ability to push other top tiers to some variant of high diff in old age
With that said, it's a pretty good callback from Sabaody where they couldn't do anything lol. B-but it also indirectly implies that Luffy might actually beat Kizaru here