He would have been trash tier, whenever Naruto's had to rely on his abilities alone he's been stomped (except his win courtesy of a fart against Kiba and his victory against the fodder mist nin). Let's examine how Naruto would have faired without the Kyuubi.
Against Neji: All of his tenketsu's would have been blocked, he'd have no secondary source of chakra to tap into and thus Neji would have proceeded to either kill him or the fight would have been stopped before that happened.
Against Gaara: No kyuubi chakra to summon Gamabunta? Sand coffin. Dead Naruto.
Against Sasuke: No Kyuubi to regenerate the lung Sasuke punctured and no Kyuubi to physically lift Naruto up off the floor out of an unconscious state to continue fighting. Base Sasuke would have solo'd without his sharingan.
Against Sasuke (Part 2): Naruto got solo'd here anyway, so...
Against Orochimaru: No borrowed power/chakra cloak to shield him from Orochi's sword=Dead Naruto.
Against Pain: No Kurama to break him out of chibaku tensei=Dead Naruto.
I could go on and on here...
Against Neji: All of his tenketsu's would have been blocked, he'd have no secondary source of chakra to tap into and thus Neji would have proceeded to either kill him or the fight would have been stopped before that happened.
Against Gaara: No kyuubi chakra to summon Gamabunta? Sand coffin. Dead Naruto.
Against Sasuke: No Kyuubi to regenerate the lung Sasuke punctured and no Kyuubi to physically lift Naruto up off the floor out of an unconscious state to continue fighting. Base Sasuke would have solo'd without his sharingan.
Against Sasuke (Part 2): Naruto got solo'd here anyway, so...
Against Orochimaru: No borrowed power/chakra cloak to shield him from Orochi's sword=Dead Naruto.
Against Pain: No Kurama to break him out of chibaku tensei=Dead Naruto.
I could go on and on here...