I'm a bit confused

[esenn1]

Well, no need to say that Rinnegan is the ultimate form of Sharingan. On the other hand, one of the basic and common prowess of Sharingan is genjutsu, and besides someone having sharingan can see through the genjutsu once cast upon him. Well, here is the problem: 1. Why Pain (who had the ultimate form of Sharingan) couldn't cast genjustu? 2- Why did he get trapped in frog song genjutsu?

I hope you guys correct me if I have missed some points

 

[Melly]

kishi made it like that maybe because it would be too OP? xd

 

[The Alchemist]

Because the Rin'negan is not the Sharingan it is a completely different Doujutsu that has it's on ridiculously OP ocular jutsu.

 

[Sir Blades]

because it was an audio genjutsu, not a visual one;which is the specialization of the rinnegan.