This discussion is kind of funny. Many people are always comparing Naruto and Sasuke when the two should not be compared in the first place. My view of the two character is simple. Unlike Madara and Hashirama who were Uchiha and Senju, Naruto and Sasuke are completely different entity. Fanboyism put aside, Naruto is far stronger than Sasuke, and this can be seen obviously by choices that Kishi make.
1. Base Naruto without Kyuubi is a match for Sasuke, but ....
Well, I added a but. As you all know, base Naruto has already more chakra and stamina than Sasuke. This is a fact, and ignoring it is a misunderstanding of the manga. The reason is clear as well: Base Naruto is an Uzumaki with a monstrous chakra and stamina. This is the reason he is Kyuubi's Jinchuriki in the first place. This is why unlike Hashirama, Kishi did not give him lot of Jutsu to begin with. If Kishi were to give base Naruto the Senju scroll as Sasuke has assess to the Uchiha tablet, base Naruto would be as strong before Sasuke as Hashirama was strong before Madara. Both Naruto and Hashirama are alike among people in their clan.
2. Kyuubi is a sea of power, and ignoring it is just unbelievable.
Well, this is my opinion. The minute Kishi gave Kyuubi to Naruto, Kishi clearly told to the fandom that Naruto was neither a Senju, nor a rival for an Uchiha. Naruto is playing a completely different role than your usual Uchiha-Senju comparison. It even seems that the fandom has forgotten that Naruto has now more power than the Naruto who cancelled all Nagato's attacks.
3. Throw in natural energy!
Yeah, throw in Natural energy and SM. I think it is clear that Naruto win very easy against Sasuke if he goes in a rage or killing mode.
Conclusion: You may get mad at my analysis, but this is a fair analysis. Assuming you have a good memory, Naruto's chakra pool without Kyuubi was shown to be the largest since day 1 of their graduation. To make Sasuke keep up, Kishi gave Sasuke better chakra control and poor chakra control than Naruto. EVery time Naruto uses Kyuubi's chakra, it is either for speed or power of the chakra. To much Naruto using Kyuubi, Kishi had to give curse seal power to Sasuke, and clearly, as the OP said, in order to match BM Naruto, kishi need to power up Sasuke with an external source. Besides, I think this will not happen. Naruto will ascend to god mode very soon.