LOL no need to act dumb, We all knew that the PK is stronger than WSS.
To be real? Do we know that? It's harder to achieve, sure, but that does not say anything about the respective roles of power in the story.
You don't need to be stronger than Roger to become Pirate King. It is arguably a more symbolic title than WSS from the way it was shown to us. No pirates "bowed" to Roger. At least none of his peers did. You need to be STRONG to reach the end of the Grandline, but you also need a fuck ton of luck. From what we know, the only reason Roger managed to do it is because of Voice of All things hack.
Roger didn't need to defeat any of his peers to become pirate King. He fought against Whitebeard more for shits and giggles from the looks of it, and the only real opponent he was shown to have overcome is Xebec and that was years before he came King with the aid of Garp. Maybe his fight with Shiki could be included if you want to be generous. But that's about it.
To put it bluntly, to become the World's Strongest Swordsman, you actually have to beat the World's Strongest. Zoro needs to beat Mihawk to accomplish his dream. Luffy however won't have to beat Roger to become Pirate King. He "only" has to get towards the last island.