He hasn't, he was able to bypass Fuji's gravity. When he went after doflamingo I'm sure he was stopped by fujitora for plot device.
He absolutely no diff fodder stomped Neptune and all of his people by himself, literally had them all tied up. And I'm positive Neptune is powerful. Stronger than hody for sure.
Kings punch was hyped to be able to take down a yonko . It was needed to push back a slab of concrete from pica.
Pica is doffys second , one of the only two characters to show full body haki. Even if he isn't that strong, the amount of stone he had , and the weight behind all of it would've been enough to easily take down even crackers biscuits. And yet Zoro absolutely no diffd him.
Also think it was plot device he wasn't going to whole cake
When Zoro has to even go over 50% of his power, which he hasn't done, after learning the baboon fighting style which even mihawk couldn't believe he defeated them and after being trained by mihawk, the worlds strongest swordsman. Undoubtedly more powerful than Rayleigh, and could undoubtedly train Zoro better at swords and haki than Rayleigh could teach liffy about his fruit, blunt attacks or haki. Zoro will be on Luffy's level or right below.
Zoro is the next Rayleigh