One point, which breaks the kishimoto logic/plot is the creation of BZ from Madara.
Lemme point it out : Madara wants to create HIS will into one Zetsu. So he knows which jutsu he needs to do so
for example : Madara wants to do katon fireball he formes the katon symbols outcome --> His Katon.
So why BZ is created ?
Its like forming katon style signs and outcome wather. Madara should have regocnized that BZ is not his will...
Because he learned said jutsu from the tablet that was altered BY Black Zetsu.
Also Hag didn't even know BZ existed, minamoto, so his comment is irrelevant.