juha already explained that it had nothing to do with trying to understand or know anything about the bankai. all that was needed was to have enough power to take it, which juha had. as a matter of fact, juha gave instruction not to engage yama before he arrived. of course they didn't listen.
but anyways, obviously juha wins this. even before using the almighty powers, juha already outclasses yama. even if he doesn't start of by taking yama's bankai. apparently juha can just straight up take people powers, he just couldn't rake ichibei's power of darkness for some reason. even still, yama's best bankai ability is his west ability. from my observations, it seems that it only stops physical attacks like from swords or the like. for instance, when ryod shot an arrow at yama instead of just letting it hit his body he blocked it with his sword. had his west shield protected him from it, there would have been no need to do so. seeing as juha has a shitton of abilities, he should have no problem beating yama in bankai even if he doesn't steal his bankai or use the almighty. we really need to see how juha was defeated 1000 years ago.
