Oda stated way back in the day that Luffy's proficiency was conquerors, and its stated by Rayleigh that conquerors gets stronger as you yourself grow stronger as you face strong opponents. It would be massive BS if Zoro, who only had 1, maybe 2, serious fights in all of pre TS and didnt even know he has this type of haki, suddenly had stronger conquerors than Luffy, who has been pushed to the limit multiple times and had multiple haki blooms

and Yamato is definitely more proficient at it so thats up to debate as well