If you remember when orichimaru fucked with the seal then you'll remember that having the kyuubu&seal ruins Naruto's chakra control. Ripping out a part of the seal made things worse since the sea was made to at least TRY and make it possible to use his own chakra. So yes Naruto would be a monster on his own without the kyubii.
The reason naruto was alot weaker in the beginning was because the seal/beast made it much much harder to do even simple jutsu than was normal for other ninjas. Without anyone with the sharringan/byakugan (other than Hinata who was too busy being distracted for obvious reasons)around to notice and tell him he never got told as a result not even factoring in the "dont tell him" rule. Even then it might be hard to notice his chakra being all screwy since they could attribute it to naruto sucking at chakra control naturally. He also had to use more chakra than normal to do anything because of the disruptions so Naruto had the deck stacked against him as far as reaching his potential power went.
He's ridiculously strong now since he can control it decently and knows how to use it properly. When Jiraya first trained Naruto he said that instead of trying to conserve chakra he should be using it since he has so much instead of trying to conserve it. This alludes to Naruto's chakra interference possibly since trying to control/conserve something that's already broken/leaking in a battle is silly when you can get a use out of the "leaky" chakra by using it when it's going out.
XI Wiki


