Zaraki is 6.67 Zettatons w/ his eyepatch, 333 Zettatons w/o his eyepatch, and 1 Yottaton by swinging his sword with 2 hands
Kinshiki upscales from Kaguya who upscales from 10 Tails Hagaromo who upscales from regular Hagaromo who's 78.2 Zettatons
So Kin has the AP advantage while Zaraki is sealed, but once the eyepatch comes off, the situation reverses badly.
Kin doesn't seem to have many hax, and the ones he does have like Karma reincarnation use Corruption Type 1 which Souls resist and implanting his soul into someone when killed. Shinigami both BFR souls they kill with their Zanpakuto and have layers of resistance to Soul hax, so none of his hax should work on Zaraki.
Meanwhile...Kin's only resistances on his profile are Ice Manipulation and Cosmic radiation on top of suppressing his ability to be sensed.
Kenpachi ironically got a few potent hax from the SAFWY Novel. On top of the layered Soul offensive soul hax and Reiatsu Crush all Bleach characters have, Kenny got passive molecular deconstruction and spatial manipulation (being able to break down space time barriers with his passive energy), space-time manipulation via being able to make holes in space-time as a byproduct of him fighting etc. His instinctive reactions in speed equalized matches make him extremely hard to hit even if Kinshiki got passed the deconstruction and spatial/space time hax (that may or may not affect the battle based on the manga, though you could argue those he fought passed SAFWY have resistances to these hax)
I actually don't think Kinshiki has any win cons here. I would say he could try to kill Kenny before he takes off the eyepatch but the molecular deconstruction. Unless we do what I said before and argue that it isn't always active based on the fights he had after SAFWY, but you could also argue everyone he fought resists those hax
