You miss the point Naruto knew he couldn't beat 3 tomoe Sasuke, He knew nothing of MS Sasuke. If we accept what you say is true Naruto said they'd kill each other sm naruto and 3 tomoe Sasuke correct. So therefore MS Sasuke stomps SM naruto its really quite obvious once you rationalise it.
He said Sasuke, not 3t sasuke, ms sasuke or any variation. He knew he couldn't just "beat Sasuke" it wasn't that simple as both of them were tied by a fate that spanned multiple generations.
You're re-writing the narrative that Naruto couldn't beat Sasuke due to him being inferior when that isn't the case. Prior to him meeting Hagoromo, it could be argued that Naruto felt he could not defeat Sasuke due to him being weaker.
The point kishi made was that they've been on par with each other since the pain arc and beyond. Whether or not MS Sasuke has a "level" on Naruto or not is irrelevant as the plot and narrative of the story supersedes your opinion on who would win.
They both kill each other or neither survive the fight, either way the result is the same.
Arguing this is asinine unless you're willing to throw away plot points and the narrative in which case there's no point in debating a vs battle when it comes down to subjective opinion in the end. I honestly cant see any fan of either side actually coming to agreement on who wins.
With that being said, it's stupid to argue this as no one is going to agree. You're going to leave this thread thinking/knowing/feeling Sasuke wins and Naruto fans are going to leave feeling the same way about Naruto.
What i'm saying is that within the confines of the plot, they both kill each other.
It's peek sage mode and open MS, but Naruto's fans excuse is he beat pain so he can beat Sasuke.
That's A>B>C logic. That's not even remotely arguable. I don't want to go into detail about who I think wins when I know they both end up dying. Maybe if this was a Spar it would be different.