In the same "talk", Kaidou swore that he'd kill BM if she came to Wano.
It was not... Garp and Sengoku know Roger and that he would never ally up with Shiki, they had entirely different goals and ideologies!
While Big Mom and Kaido were allies and friends back in the day and literally openly talked about an alliance - chances were high they would ally up, which ended up happening.
Everything you say speaks against any sort of logic and facts. And you keep ignoring 90% of my posts cause you know you cant say shit against it, instead keep on insisting on the one least important point of the discussion - and even there you realize how wrong you are. Tell me a single other occasion an Admiral was "formally" sent out when 2 Yonko meet up, I wait... Literally didnt happen in the meeting of Shanks and Whitebeard which is the most prominent and obvious on screen meeting of Yonko we saw so far.