Board Thread:Naruto Discussions/@comment-28294008-20160424155402/@comment-734582-20160526080627

Sage mode requires there to be spiritual and physical energy to counterbalance. If you're dead tired, then that means none of that is present. Naruto couldn't enter sage mode.

Naruto and Sasuke have always been closely matched. Not minute-to-minute, but over the course of the series they were close. The final battle was a tie, it was intended to be a tie.

Sharingan and Rinnegan have powers that make them excellently suited to using others, like how Madara used Kurama. It's a strength in itself, not a weakness. Sasuke's raw power may not match Naruto's, but ultimately their total strength is the same.