No you don't lmao. Just like Roger ran into Big Mom's territory and ran bag out straight after, never having fought her. To become the pirate King is to find the last Island, and can be done which ever way and not just through strength. You can't be the strongest if you need help defeating said current strongest, come on man
. Defeating the world's Strongest creature (after said creature fought 15 other people) will not make Luffy the world strongest creature, that would still be Kaido (if he is left alive) as luffy ain't a creature/zoan. Luffy defeating blackbeard is headcanon, anything can happen and he's not the world's strongest ever either. Headcanon again on defeating Akainu and Imu. And who says Imu can fight?
So far luffy defeating Kaido, eventually is the only correct thing you've said.
Luffy will only hold the title of Pirate King and that's it