When has Zoro ever cleaved anyone in half? He’s not killing Shiryu nor Mihawk and he will have much stronger AP by then. He might even need multiple acoc hits before they go down. Endurance is a a much more important stat at the end of the day. Teach also has stronger haki than King, the high-tier… so that helps with his defense.
Current Zoro is also not even close to BB, you’re deluded if you think he is. If you think that Asura is strong enough to one shot Teach then he won’t ever land it. If you think Zoro can land an Asura then Teach won’t get one-shotted by it and will proceed to beat down Zoro’s ass.