Sasuke and Naruto are meant to be the most POWERFUL ninja ever during their final fight (the last fight in the series), as of right now, Naruto would wipe the floor with Sasuke unless he gets a significant power-up (perfect Susanoo).
It sucks because we haven't even seen the extent of his EMS yet but it'll probably happen regardless.
Why would it be alright for Naruto to receive Rinnegan but Sasuke not? Sasuke has Sharingan, which evolves into Rinnegan, Naruto has Sage mode, if he were to combine it with the fox, he would have enough to counter or equal Sasuke with Rinnegan.