Sasuke wins low-mid difficulty.
-Sasuke can summon his hawk to gain an aerial advantage and move at speeds quickly enough to dodge incoming bijuudama
-His versatility with enton (enton arrows, shuriken, etc.) means that he can quickly ignite Bee's BM form on fire all over his body - Bee can counter by cutting off the affected tentacles, but it will be difficult to deal with so much fire all over his tentacles, and he's finished if it hits his main body. This can at the very least be used as a distraction
-V3 Susano'o slices tentacles in half like butter
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and probably can chop up Gyuki's main body with little trouble, coating susano'o with enton increases attack power
-Aoda can assist by wrapping itself around Bee's tentacles to restrain him, giving Sasuke an opening to land an attack
-Susano'o arrows slice through Gyuki and can KO him if they go through the head, Bee won't be able to dodge quick attacks like this in BM form
IMO a fully rested MS Sasuke (who has experience using his MS techniques, like when he fought Danzo) is enough to take down Killer Bee.