That's because Tsunade can heal herself but Neji can beat before she heals herself unless she uses creation rebirth but she cant use it for long or she shortens her life span too much.
Naruto has surpassed Jiraya and Sasuke surpassed Orochimaru experience dosen't mean anything in Naruto.
Neji has 3.5 in stamina Tsunade has a 4 that's not much of a difference.
Neji's byakugan sees chakra so if she doses he can counter with gentle fist.
Your acting like if Neji is a distance from her his going to waste chakra trying to hit her Neji is a close combat fighter and is too smart to do something like that.
Im not talking about her with Katsuya she fights Neji with her own powers.
Experience means so much and you're underestimating that. Experience enlightens, gives wisdom, not just skill.
This isnt' canon but it's a lesson none the less the eternal genin, he knows the ropes, he knows how things are done, he's been around the block since the Second Hokage, he has years of knowledge and experience on his hands that aids him. Jiraiya and Orochimaru have things Naruto and Sasuke don't have even if they'd still loose to them (and Orochimaru leeched off of Sasuke, Sasuke took him down in a weakened state yet Sasuke was obilvious to Orochimaru still remaining inside him, Itachi defeated Oro, Sasuke acted as a vessel for the parasite. That shows you experience and learning from his mistakes as well)
Now Tsunade can hold her own with her creation rebirth for as long as she wants until she dies and she's not going to die in the span of one battle with a jounin, not in the time it would take for Neji to exhaust himself and end up loosing to her, that is a given.
Neji can't control his motor movements corectly if he's hit with her body pathway technique. He'll need time to figure out the movements of his body to know how to correct the issue just like Kabuto did and that is a huge halting factor for him.
Constantly trying to get to her, avoiding her attempts to launche bolder sized sections of earth and what not are.
Rotation isn't going to be something he can keep doing forever and here's a scinerio for you. if he begins rotation, if she launches a punch to the ground, what stops him from loosing his balance?
Katsuya is part of Tsunade's weaponry, she can use her if she want. IF Tsunade uses Katsuya, Neji is done as well
IF Tsunade uses her creation rebirth, Neji is done as well because she can keep it active long enough to fight him and defeat him and if he gets close enough to her to be hit, which he'll need to do, IN ORDER TO hit her, he's done as well.