In Fishmen island, according to Oda's SBS about CoC haki, Oda estimated that Shanks(and Rayleigh) could have knocked out more than the double Luffy did, although stating that it can't be evaluated in number, but I think it implied that time skip Luffy was about 50 times stronger
And through the dressrosa, WCI to Wano gauntlet, Luffy became a top tier, with Rayleigh mentioned to be 100times stronger than their preskip self, so in terms of overall lvl, this estimation makes sense. It doesn't mean however that top tiers are exact equals. Hence why we have old Rayleigh losing to Blackbeard due to old age, Kaido being the strongest before his defeat, etc