The chapter you are referencing has to do with the activation for the SHARINGAN, not the Rinnegan. They share nothing in common beyond being part of an evolution chain that is extremely diluted.
What do you not understand about my easily worded statement? The only reason that the Uchiha's have said Yin manifestation is due to Hagoromo splitting his chakra into Yin and Yang between his son. It is directly linked the Juubi (The Sharingan) due to Hagoromo's son (Elder). Getting his Yin from his father is essentially getting pure Yin from the Juubi, and that gave rise to the Sharingan down the line. If someone (Naruto) were to reconvene in this case; the Juubi's chakra, he would achieve the similar if not outright same effects that Hagoromo had when Kaguya bore him; the Rin'negan. It is essentially the same concept as recombining the Senju and Uchiha DNA to awaken it. They both originate from the Juubi and would yield the same result; the Rin'negan.
Yes, I agree, but let's all remember that Hagoromo initially didn't give his Uchiha ancestor the "Sharingan"
We all know that the Sharingan came after, he gave him his dojutsu which doesn't look like a Sharingan, it doesn't have tomoes. That dojutsu pre-Sharingan is the pure manifestation of Hagoromo, not Sharingan. Sharingan is a trait of the Juubi, not of Hagoromo. Juubi didn't have Rinnegan.
Just wanted to point this out. Still undecided whose theory to believe. Go on.
On-Topic: Good topic, but you pointed that the Bijuu had less power then and so the Juubi. Yet, the Juubi wasn't a smaller weaker form then, that's just an unbiased assumption. Also, when Minato took half chakra of the Kyuubi, Kurama didn't look younger, closer to the form when Hagoromo spoke to them, but rather just smaller in size, which is basically un-related. Kurama in his Bijuu-yers, is somewhere in his 40's, from they way he talks and all that, or even younger. It's hard to imagine that, in Bijuu-years, a 20 or less aged Kurama would look the same.
I also believe that Hagoromo wanted to leave them like that, so that they can experience from how it is to evolve in this world, to grow up physically and mentally, with the power basically remaining the same. This can't be considered as a fact in the conclusion that Hagoromo is weaker than Madara. Creating the moon without the Juubi, after extraction and spreading all 9 Bijuu across the globe is the simple Manga fact that his power is un-equal. He had the purest chakra, the most powerful one. He was the only pure Uchiha and Senju, which no one else can be. Implanting Uchiha DNA or Senju DNA is nowhere close to actually being one.
