Kishi tries to shove down our throats how Rinnegan is better, but then fails to show anything noteworthy from it and has Kamui be much more useful.
Like, Obito said he'd have installed double Rinnegan... Dude why, for what reason? One Rinnegan already gives you all the skills you can use, and you didn't bother even using them anyways.... If he had 2 Rinnegan, he'd have been destroyed. If he had Kamui phasing when he became a Jin instead of shitty Rinnegan who's there only for design, he'd have been complete boss and had won the war.
Ask Sasuke what good his advanced Rinnegan was against Kaguya... Look at what Kakashi does with the lesser DMS and few Rikudo chakra...
Yeah, Madara would have been untouchable. If you ask Kishi, he'd have been weaker, but at the same time he'd have drawn Madara as stronger and with better feats.