Under more careful consideration its highly likely that neji can low/mid diff scenario 1.
-With byakugan and pre knowledge of gaara's powers along with the ability to destroy/ destabilize the chakra in chakra based substances , he can effectively sabotage gaara's gourd sand without gaara even having s clue to ways going on until his sand is too soft and slow to save him , this can effectively stop the use of sand dome before it even begins since neji would kill gaara the first chance he gets.
-Neji can also possibly expel the chakra field used against kido to divert his ultra fast arrow and which gave neji sensing , he can freely control the chakra around himself even going so far as to remote control it into his blind spot.
This method can likely be used to dismantle gaara's gourd sand even further when combined with neji assaulting the chakra in gaara sand with every strike and if gaara even tries to counter neji in close quarters with sand then neji can expel a large enough chakra shield about the sizr of his kaiten without the need to rotate
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This can easily stop the sand as even weakened base Lee along with sasuke and naruto tanked hits from his transformed state without much injury , neji doing the same as Lee did here with pure thick chakra would easily stop gaara's sand as that's the inner function of the first stage of kaiten ,stopping shit from hitting you.
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Also stops him from getin sangwedged by sand and adds even more pressure to gaara since he rarely moves and will be forced ti tango with an object that can't easily be moved or forced to evade his sand counters in cqc like sasuke/Lee which is probably why gaara has this not so smug look on his face here , kishi did this for a reason and had gaara's brother lable neji a fellow monster without even seeing a hint of his power.
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Neji wins mid/low diff.