As the title says but unfortunately it seems like rinnegan is not rare anymore and every rinnegan villian is being soloed by naruto.
Naruto has already fought and defeated all of them except 2 rinnegan eyes madara:
-Pain (Rinnegan user)
-Obito (Had rinnegan and used Outer Path)
-Madara (Defeated 1 rinnegan eye madara. Didnt defeat 2 rinnegan eyes madara though because of BZ intervention)
-Sasuke (Rinnegan user)
Now naruto is going to fight and take more rinnegan users down:
Underlings:
-Momoshiki
-Kinshiki
Main Villian:
It also implies that Rikudo Sage Mode is really rare 
. Every unique ability is rare that's the reason RSM is only belongs to naruto U_U.