And yet everything afterwards says Yamato is above the Flying 6....
Your logic is faulty.
Well she can still be stronger, right ?
They needed to prove themselves to get a chance to fight an All Star, but if they can't, then they are not worthy.
Nothing wrong with Yamato > F6 and the F6 being unable to complete the task and get their chance to fight an All Star.
It's also possible that Yamato is being underestimated by Kaido, so this speaks more about their estimation of Yamato's strength, than it being concrete evidence of where Yamato stands strength wise.
It's interesting to look at Yamato's perceived strength, and see where she ends up afterwards.
You don't have to be defensive about this if you like Yamato.