Rinnegan without the Tail Beast is an under power eyes that eat up your chakra over time and you end up like Nagato did Young but worn out,why do you think He use courses for each path. Sasuke can get the Rinnegan and get His Butt kick by Naruto and His Tail Beast power and if you have all the Tail Beast you get the Rinnegan as the SO6P did and you know Naruto is the next SO6P.
First of all,
Nagato became worn out because he was drained by the
Gedo Mazo statue during his first summon of it. He was unable to fully control the statue as he lacked the power of the
Uchiha Clan. He also may have had a huge chakra reserve because of his
Uzumaki/Senju lineage, however he did also have a very poor quality chakra. A
Uchiha has perfect quality chakra, so they can easier stable it and use less chakra on each attack. ( Theory )
Sasuke is getting
Hashirama's Cells which will boost his chakra reserves and since he is an
Uchiha, all that chakra will be top quality. An
Uchiha with
Senju Power can easily rival the power of the
Bijuu's in the term of chakra.