The Itachi Shinden novels gave us new info about the byakugan. Itachi and Shisui fought a byagukan user named mukai and 3 things occurred that made me think back to this potential fight. #1 A Hyuga can read the flow of chakra and use gentle fist to easily split a giant fireball jutsu in half. Mukai described this as something “easy” to do for a gentle fist user. Neji has a better feat of using razor sharp precision to cut kidomaru’s webs, neji can split chakra based substances in half .#2 Sharingan genjutsu doesn’t work on the byagukan. The byagukan eye perception is so fast the sharingan cannot lock them in a genjutsu. Shisui needed the mangekyo sharingan because it can trap the under a genjutsu in less than a thousand of a second #3 The Byakugan kekkei genkai is stated to be a visual jutsu on par with the Uchiha sharingan. There’s another statement like this in part 1 where kakashi says in perceptive ability it’s above the sharingan. Neji can potentially cut fireball jutsu in half given his level of gentle fist on top of him being the biggest genius of the hyuga. He can use rotation as defense, neji can’t be put in genjutsu (not that Sasuke could use genjutsu at that point anyway) and once neji cuts sasuke’s chakra points it’s over. neji would’ve won this fight