Then it would seem as if though Kishi is downplaying Sasuke's abilities.Yes exactly. I agree completely. Naruto will show them the right path, which is for them to be accepted as a partner, not as a weapon.
Well naruto will most likely hold this mode for a certain time limit. He will most likely be god level just untill he beats madara and then He will lose it finally equaling him out with sasuke.
This is the most probable solution.
Anyway in the final fight i would love a DSM Rinnegan Sasuke vs Ten-Tails Naruto, it will never happen though.