Compared to MS, it didn't seem so OP.
Koto and Kamui and PS outshines anything Nagato had
KA was seen with the Byakugan. What makes you believe Rinnegan, the highest doujutsu that can also see chakra networks would not have been? PS is a jutsu and Preta path and onmyouton cancel jutsu. Kamui has a time limit and cool down and can be outsped, possibly even by deva path.
It's because it comes as a set. A set that only works with the original user. It can't really function well on its own, unlike MS which still at least retains it's techs.
Perhaps, or perhaps the rinnegan without nine tomoe is incomplete or Nagato did not have sufficient chakra, skill or lineage to wield it completely. He ws also not the one who unlocked it.
With MS, at least Danzo was able to still use koto.
Danzou had the chakras of a hashirama clone and eleven other Uchiha combined.
Rinnegan on the other hand loses almost all it's power once separated.
Says who? Perhaps you didn't see it destroy an army, summons sannin levels summons, conquer a nation, blow up all of konoha, fight on par with and restrain the kyuubi, suck out people's life forces, read their minds, absorb any and all jutsus and summon meteors from space?
In all: steal Shisuis eye, you get his tech.
Steal Madaras eye, you don't get anything close
You are forgetting Limbo and all the MS techniques Madara retained with his Rinnegan.
