Kenpachi could beat him...
no that would be a lie. every one says kenny kenny kenny to every one when all he has is his spirit pressure and its shit to ymichickas. fuji kujakus power in this true form entangles his opponant and sucks out any spiritual pressure and transfers it to yumichika so no in that case kenpachi = dead.
any yes i understand between strength and unbeatable ness... but there is differnt measures in strength.
this is one time where I think Kenny Kenny Kenny fits
first for all the over rating of Kenpachi he still get underrated in one thing
He is smart, when he fought Touse and his "auto kill sphere" he beat him with his brain not his Uber SP
his Uber SP is his other advantage in this fight
There is just so much SP it would take a while to suck it all up giving Kenpachi time to think up a counter
also consider could Yumichika handle all that SP
think back to the begining of bleach when Ichigo fought the Menos he released so much SP that he could not move and If Ishida did not step in his zanpukto would have shattered