you missunderstood his statement (on purpose?).
He expect him to win, otherwise he would look down on him. He wouldn’t take Luffy serious anymore.
In Kids point of view, he and Luffy will beat a Yonko here.
No, Kidd won't take down anyone.
He is just the bargaining type, from targetting Shanks to targetting Kaido's head and now stalling Big Mom together with Law.
There is a reason Kidd doesn't fight Big Mom alone, but with Law.
It is so that Law can witness and relay the message to Luffy in act 5, that Big Mom has kidnapped Kidd.