Yep, my theory was wrong.
I am of mixed feelings about this one. I like that Unohana is cheating, but I hate the reason that she's cheating. Kenpachi gets stronger when he almost dies because he's such an amazing unstoppable superman that he's been unconsciously blocking himself forever in the hopes of getting worthwhile fights.
He's already an awesome badass, Kubo, you don't need to make him just that much better than everyone else by having him be stronger than the best swordfighter in Soul Society however many hundreds of years ago when he was just a kid.