no...you don't have to be their level to injure a little.........Kinemon can cut fire and has ryo...and who said Kiku ain't commander level?...how did you know?? same goes for Izo, he was one of the WB commanders....
In this case yes you need.
Why? Because Kaido is an equal to BM in terms of durability/hardness of their body, without the need of Haki. Even above with his hype.
Any other character would be fine, I mean, if scabbards injure like this Shanks, WB, Roger, Garp, Sengoku, Mihawk, etc etc (without them using CoA), this won't be a problem, since they don't have this "special" body.
But with Kaido there is, he has a natural strong defence without the need of Haki. He even asked, why are they able to injure me despite not being as strong as Oden? -> Implying you need that lvl of AP.
The same face got we the people who payed attention to these details.
Brook injured BigMom homies which I don't think Kata/Doffy or King (?) can do so Brook is stronger than them? or Sugar can neg diff the entire verse eventhough she ain't even half strong as Doflamingo....
Brook's ability is counter to BM's ability. So ofc he would do better than those you said.
But here scabbards don't have any counter for Kaido. Their attacks are normal cuts. Advanced Haki first lvl increases AP only, more than normal CoA.
If you have 50 points of attack normally, with normal CoA it would be 70, and with Advanced Haki it would be 140 let's say. There is nothing special about it.
So Oda does not make sense at all. In the previous arc he needed to nerf that durability of BM with all that stuff about Carmel and BM's mental state, and here scabbards are cutting Kaido because reasons!