Whatever Kaido thought, it is superseded by this:
Yamato's debut was low diffing a Tobi Roppo.
Immediately after that, she "won" against a pissed off G2/G3 Luffy:
(Luffy wanted to get past her, while Yamato wanted to make him hear her out. Luffy gave up fighting her and listened):
Yamato defeated Luffy while bearing him no I'll intent and making no attempt to fight back:
What Oda showed is that Base Yamato low diffs Tobi Roppo and is considerably stronger than Post Udon Gear 3 Luffy.
The Tobi Roppo being asked to capture her is irrelevant for gauging her combat ability given such a clear indication of where she stands in relation to them.
Perhaps, Kaido and King simply
greatly underestimated her. After all, I doubt they would send the Tobi Roppo if they knew they'll get low diffed.
Alternatively, Oda changed his mind on how strong Yamato is supposed to be.