Killer Bee is powerful and there is no denying in that but the problem is...the form that accesses Kirābī's full power comes also with an disadvantage as it makes him too large of a target for Itachi's fast techniques.
Itachi takes this, Killer Bee's 8 Tailed form is vulnerable to the attack of the Totsuka Blade which seals anything, Yata mirror deflects TBB. If Itachi is fighting with intent to kill he can kill Bee.
Itachi wins mid diff. Amateratsu will stall Bee long enough for a Totsuka swing. And Itachi's Tsukoyomi does work on perfect jinchuriki's because it manipulates time. Hachibi has a reaction time as well, he has to disrupt the flow of chakra, by then, at least 1 second would've passed, which should be about 24 hours in the Tsukoyomi world.
If Yata's hype is true, it counters any number of BijuuDamas Bee can shoot. The Hachibi has shown no special tanking feats, it got sliced up by GOD DAMM SHURIKEN. Totsuka Blade, GG.