There's no reason a 9 tails jin and a rinnegan user should be stronger than a juubi jin with double rinnegan and a 3rd eye.
Thats just bad writing. naruto and sasuke being stronger than a juubi jin despite them having THE EXACT same powers as the juubi jin is worse than Ultra instinct.
I havent seen a power scaling this bad. like ever.
What in the world are you talking about though?
Neither Naruto nor Sasuke are stronger than a juubi jinchuuriki even in their adulthood. They can put up a fight against a juubi jinchuuriki, but they can't win.
Rikudou Madara would wreck both Naruto and Sasuke individually.
I think you are taking the few hits that they got in against him a bit too seriously.
Do remember that Madara was both injured and nerfed (missing one rinnegan, and most of his truth seeking balls) when Naruto launched that lava style rasenshuriken at him.
When Sasuke got in his few hits (that sword stab and cutting him in half), they were impressive, but please take into account the fact that they didn't really affect Madara that much. Madara casually brushed both of those attacks. Sasuke never actually landed any battle ending debilitating blows on Rikudou Madara. Also, that was still a nerfed Madara because he did not have his other rinnegan or his other truth seeking balls when Sasuke landed those blows.
Once Madara got his other rinnegan back, neither Naruto nor Sasuke landed a hit on them. Madara attacked them with limbo clones and chibaku tensei meteors before casting infinite tsukuyomi (which would oneshot Naruto by the way). Sasuke would be oneshotted by juubi bijuudama (which Kishi simply didn't let Madara use as just another form of nerf).
Rikudou Naruto > RSM Naruto and Rinnegan Sasuke
Even in adulthood, Naruto and Sasuke would still lose 1 vs 1 to Rikudou Madara. This especially holds true for Naruto who at this point may or may not have RSM. It is hard to tell because Masashi nerf-o-moto just had to go and stupidly make adult Naruto use a mode that looks mostly like BSM, but has a few small visual traits of RSM such as the lack of pigmentation around the eyes while still retaining the cross shaped pupils, or the shortness of the cloak (although Hokage Naruto's orange jacket is short anyway, so there goes that point). What's more, he just had to remove the truth seeking balls and not have Naruto use any of the bijuu KKGs, or even make any verbal mention of having the bijuus inside of him or having RSM! If I sound salty about that, it's because I am to be honest! I hate that Kishimoto did that to Naruto!
I digress though. The bottom line is that Neither Naruto nor Sasuke can beat Rikudou Madara (or even Obito for that matter).
Now if your gripe is that Naruto and Sasuke can put up a fight, I still don't understand why you would see that as illogical.
Naruto and Sasuke both received half of Hagoromo's power (and Hagoromo was already around juubi jinchuuriki level even before he became the jinchuuriki). It makes sense then, that Naruto's and Sasuke's power levels would skyrocket to six paths level.
You say that a Kurama jinchuuriki shouldn't be stronger than a juubi jinchuuriki (which he isn't), but keep in mind that Naruto wasn't just a Kurama jinchuuriki when they fought Rikudou Madara.
Naruto contained the power of all 9 bijuus + Hagoromo's chakara. Therefore it wasn't really a Kurama user that was approaching Madara's level. Rather, it was more like a pseudo juubi jinchuuriki that was approaching Madara's level. Both the databook and even Sakura Hiden describe Naruto as being "like the 10 tails jinchuuriki" or being "a living vessel for the power of the 10 tails".
As for Sasuke, he too isn't just a rinnegan user. He is a 6 tomoe rinnegan user with half of Hagoromo's chakara. That makes a huge difference.
Even then though, like I said before, Madara still beats both Naruto and Sasuke in 1 vs 1 fights. He could most likely also beat them 2 on 1, but if Naruto and Sasuke had the seals, then they could seal him in a 2 on 1 fight.
One more thing:
Ultra instinct is epic!
