An chakra exhausted Naruto who had an unknown amount of energy drained from him. Sasuke's shown that opening a portal to different dimensions doesn't take away his abilities right away as seen in the manga and the movie. Even then, it's not all that surprising that Sasuke can use his chakra to enhanced his physical power given his level of chakra control.
That was before Naruto's power increased further by gaining Hashirama's cells and Kurama's full power. I'm not so sure that Sasuke's Susanoo would be its equal now.
Yep.
I doubt he was on to creating a new element honestly.
Yes he did, but he'll never be able to use them like Naruto.
Didn't Naruto gain the ability to make his arm intangible which leads to him probably pulling anyone's chakra from their body?
Is it really all that surprising that Sasuke was behind Naruto in power?
He acknowledged that BSM was above him before him and Naruto received Hagoromo's power. Obviously, that means that Naruto was still above him in overall powerpost power up , all you'd need to do is look at their performance against Kaguya.
Naruto could clash against her briefly. Sasuke's Susanoo gets destroyed easily.
Naruto resisted her hold on him whereas Sasuke couldn't.
Kaguya/Black Zetsu acknowledging themselves that they didn't know how to deal with Naruto.
Naruto plowed through the chakra hands that destroyed Sasuke's Susanoo with no problem.
Sasuke couldn't hit an chakra exhausted Kaguya whereas Naruto could blitz her.
With all of the above being stated and shown in the series, it's reasonable why Sasuke needed to catch up with Naruto's power, which he did by adulthood