shes not really an under dog she was stated to have talent in chakra control and genjutsu in part 1 she just never trained to gain new jutsu she didn't try and train to get stronger in part 1 until sasuke left, the sound chick even told her she shouldn't of wasted so much time on her hair and learnt some jutsu. she was to shallow and vain to care before that.
while naruto in part 1 was constantly training to better trying to overcome the hatred that everyone gave him. he learnt shadow clone, rasengan and summoning in that same time sakura learnt nothing. he couldn't regulate his chakra because of kuramas influence but he still kept on struggling to overcome this handicap no one believed in him most were rooting for him to fail or worse die. he kept on and slowly and against the odds changed peoples feelings towards him.
Part 2
Sakura learnt CES and healing then didn't learn anything for 400 chapters, still hid behind others and emotionally manipulated naruto.
Naruto learnt rasengan variations, fuuton rasenshuriken, mastered sage mode and all its techniques beyond all previous sages, learnt his heritage (even though he didn't inherit his mother or fathers talent) defeated kurama and gained kcm, freed kuramas of his hate gained bijuu mode, befriended all other bijuu, then combined sage mode and bijuu mode into bsm.
Narutos heritage: mother sealing abilities and life force
father rasengan, sage mode, Ftg and sealing
Ashura a reincarnated spirit possessing him whos only ability is a kind spirit and the ability to draw people to him.
naruto hasn't displayed uzumaki sealing jutsu
hasn't anywhere near the natural talent of minato
ashura doesn't pass abilities as it was implied he was always weaker than indra
naruto hasn't gained much from his heritage apart from his affinity with bijuu and his life force.
naruto was the true under dog had less talent than sakura but surpassed her with hard work. sakura was just lazy and to weak to utilize her talent efficiently.
