He was taking Luffy serious, he even said that he not underestimate him.
Katakuri himself said that he was using stronger haki form, Luffy clash with Katakuri before and his hands didn´t get hurt:
After that Luffy hands didn´t get hurt and Luffy also said this:
Katakuri clearly lvl up his hardening, same did Jinbe.
Luffy hit Katakuri: Scream in pain when he use his adv hardening.
WsW pierced Jinbe, Jinbe use adv hardening: He broke his finger and scream.
Their is clearly a similar thing, with both Kata and Jinbe.
And the top of adv hardening is what Mihawk have, black blade.