He didn´t, whole wano believe that Momo and co getting killed to in the fire.
Listen what Marco said in this chapter, they know about Oden death after years passed away.
In that time Oden,Momo and the other where dead, no one know about the 20year timetravel.
WB didn´t state that they losing against Kaido, they said they would lose many people on their side, the same thing Kaido basically did with Oden when he didn´t fight Oden and Hyo in sametime because he fear of losing many mens.
And it would speak against Wb character to risk his son lives for nothing, Oden was dead as the other family members, their was no point to risk a totally war. WB didn´t even get his revanche against BB because he had bad feelings about it, tells alot why WB didn´t a war.
Nothing about him beeing weaker then Kaido, if you accept that as fact then Oden was stronger then Kaido too, Big mom also since in both way Kaido fear to battle them because of losing them.