neji was trained by his uncle who isnt really the strongest guy ever. sasuke was trained by orochimaru who is a sannin and knows like a billion jutsu, also sauke can use his sharingan to further his jutsu training by being able to copy them and learn them a lot faster

neji trained with distractions like becoming jounin and various other things such as friendship, sasuke trained with nothing else in mind but getting stronger, its just him oro and kabuto and i doubt they went on many picnics