Okay I was prepared for someone to bring this point up, YES the kyuubi has been a huge boost in Naruto's power when he needed it. But it was completely different mainly because there were consequences for it being someone else's power, Sasuke's Susano'o, from what we can see basically just depletes his chakra and slowly damages his vision (and no not permanently because just like every other time Sasuke has had a problem, kishimoto writes in a magical solution, being Itachi's sharingan transplant, I also was never very clear on how someone can have eyes transplanted into them when they already have eyes but whatever...) but back to my point which is that Naruto had like zero control over the Kyuubi in part 2, I'll admit that in part 1, he was really able to use it to his advantage. But then in part 2, Naruto can't even see straight in his one tails, I mean its almost comical how much energy Naruto wastes once he is using the Kyuubi's chakra, then theres the fact that he can't tell friend from foe and THEN theres the fact that its basically taboo to use it because the ninetails could go nuclear and completely take over, so to some up the ninetails power is more of a liability in shipudden than an asset, which is what makes him stop using it almost completely from after he attacks Sakura until he loses it when Hinata almost dies. Now how Kyuubi's controlled chakra will help him in the future, only time will tell since we haven't really seen it in action yet.
Now onto Sage mode, yes sage mode is superrr cool and it boosts basically all of his skill (probably giving himself just a slight edge, if any over sasuke) but there is a huge drawback, it only lasts for five minutes unless he has time to prepare clones beforehand to meditate and accumulate nature chakra (and seriously, when will he ever have time for that again)
And with the brink of death point, Sasuke has got Naruto waayy beat on that count I mean it is so unfair 1. with his fight with Deidara, Sasuke somehow has enough time to summon Manda, cast a genjustu on him, then crawl into its stomach and reverse summon him??? Come on people I mean Naruto either gets his ass kicked or he kicks ass but rarely anything in between. But sasuke just walks up to Akatsuki guys that no one has been able to beat and is just like "hey tell me what i wanna know and I won't beat your ass" 2. Itachi sooooo had him beat I mean Sasuke looked like he was about to crap his pants when Itachi was walking toward him (yes I know that Itachi had no real intention of killing his little brother but now everyone is like 'bow to the mighty Sasuke, the slayer of the great orochimaru and powerful Itachi, when in reality, yes he fought hard but they were both flukes, Sasuke even admitted this about Orochimaru. Then we go to the five kage summit, where by this point his ego is so over-inflated that he thinks he's unbeatable 'five kage? ha no sweat, give me ten minutes' is his attitude and people actually BELIEVE IT, both Bunjiro and Ao from the mist made a remark or possibly a thought that was like 'Uchiha Sasuke? the one who defeated Zabuza and Haku?) HE DID NO SUCH THING AND ITS RIDICULOUS THAT PEOPLE WOULD EVEN SUGGEST IT, LET ALONE BELIEVE IT!
and look I'm seriously not a Sasuke hater, he is actually a pretty good character and the complexity of the adversary relationship with Naruto makes it so much more interesting than your 'run of the mill' bad guy, I am totally willing to say that Sasuke worked his ass off when he was younger to compete with Itachi and then even more after his clan was annihilated. BUT, what I'm trying to say is that it really irks me that Sasuke is just generally better at everything, without really trying at this point and Naruto is ALWAYS then underdog, in EVERY fight, it just gets tiresome I guess. I have rambled quite a bit here but I mean every word