Honestly, I just interpreted it as Luffy saying he's become strong enough to face Kizaru head-on and the 100× thing, while indeed a call-back to Rayleigh, isn't an exact measurement of Luffy's capabilities. If Oda was saying G5 Luffy is only as strong as Old Rayleigh, he'd say that, instead we had this version of Ray highlight he wasn't capable of beating Teach. In his prime, I completely understand comparing him to pretty much anyone but I think it's overexaggerating by taking a callback and saying it means more than it does.
Regardless, we'll see Luffy face Kizaru now, not like vague statements are gonna change the outcome of this match. I just think the line is meant to show the progress of Luffy's crew as a whole, not that Luffy's restricted to Old Rayleigh level.