Marco is stronger than Katakuri. If they fought, nobody in Katakuri’s family would consider Katakuri to be invincible because Katakuri would have lost. I know you want to picture glorious Katakuri defeating people like King, Beckman, and Marco but you need to start small. First we need Katakuri to be able to defeat WCI Luffy and then we will work our way up to more powerful opponents. Got to learn how to crawl before you learn how to walk.