Well, when we scale in the battledome, we don't take haki blooms and PIS into account.
Also, I think you misunderstood the Zoro and Killer parts. Zoro did use ryou/barrier haki to cut Kaido. Killer cut Kaido using hax, he has sound based hax which bypasses the scales entirely.
Think of Kaido's scales like a screen - even Kiku's ryou/barrier haki attacks can bypass it but a normal CoA infused KKG cannot. Inorder to bypass that screen, you either need ryou or other hax (like Law's internal attacks, like Apoo's internal blasts, like Killer's sound based waves etc,) or Advanced Conquerors.
And Advanced Conquerors isn't something entirely different from ryou/barrier haki - in Ryou you flow CoA outside your body like Hyogoro explained. In advanced Conquerors, the concept of flow is the same - you flow Conquerors haki instead, as Luffy explained in chapter 1010.