I don't buy the stuff with the previous Zaraki's fights. It ruins the shit Ichigo had to overcome. During their duel Zangetsu talked how Zaraki's sword is just a tool and how this is their key to the victory, but now Kubo says that all that wouldn't matter had Ken-chan been at his REAL power level. Also, with Noitora he used his kendo skills(which from what I heard don't work that way, but I digress), not some power up, he could use it from the very start. He later on killed the strongest one(with tagteam with Byakuya) without breaking a sweat and said it was "boring" when he supposed to unconsciously restrain himself.
So while i believe that twist with Unohana was carefully planned I find the mention of the previous fights just made up right now.
EDIT: Also, is she really killing him or is that poor translation? So she has power of resurrecting as well?