Momoshiki was absorbing God Trees abd other otsutsuki too so... But no one can have rinne without having had a sharingan thats what the manga shows... Ocular power comes from Indra's migrants not from Ashura so none of his descendants can get it they would get what naruto got and Indra's would get whats sasuke got...
You have to have a ocular power in order to fet the rinnegan... All otsutsuki, who had rinnegan and the uchiha who had rinnegan all had a ocular power, you all think someone who never had any ocular power all of a sudden can miraculously appear a rinnegan are stupid thatd impossible thats why the manga shows people with ocular powers are the ones awakening rinnegan
Bold: The manga never showed that. That is just fan assumption based on what we've seen. However, when talking to Naruto and Sasuke, Hagoromo only said that you needed to assimilate both Indra's and Asura's chakaras to awaken his own chakara and get rinnegan. He never said that you needed Indra's chakara + Asura's chakara + sharingan.
This fact is further supported by the fact that when Madara awakened the rinnegan, one of his eyes was blind and ineffective due to his usage of izanagi. Yet Madara still awakened rinnegan in both eyes.
The only reason why it seems like you need a sharingan to get rinnegan is because aside from Hagoromo and Momoshiki, Madara and Sasuke are the only known people to have awakened the rinnegan, and they are both Uchihas that possessed sharingan.
However, it is notable that Hashirama and the Senju clan never had a tablet like the Uchiha did, so they had no way of even knowing how to go about obtaining rikudou level power. As for why Naruto got rikudou senjutsu and not rinnegan (and why Sasuke got rinnegan and not rikudou senjutsu), we can't really say. My personal theory is that Hagoromo actaully just gave Naruto and Sasuke rikudou chakara and seals, and by doing this, he simply awakened the powers that were already imminent for Naruto and Sasuke.
Here's what I mean: Before even meeting Hagoromo, Naruto already had the powers of all 9 bijuus as well as senjutsu. Hagoromo's yang chakara was probably just the push that Naruto needed to mix this combination into RSM. Similarly, Sasuke was already born with Indra's chakara, and he received Asura's chakara via Hashirama's cells from Kabuto just before meeting Hagoromo (there was also that chakara gift that Hashirama gave Sasuke). Hagoromo's yin chakara was probably just the push Sasuke needed from there in order to awaken his 6T rinnegan.
In short, I believe that Naruto and Sasuke both got what they got because they had the ingredients for the specific thing that they got, and because Hagoromo gave them yang and yin chakara respectfully. This is just theory though.
Digressing back to the point though,Hagoromo's statement that you simply needed Indra's and Asura's chakaras, combined with the fact that Madara awakened rinnegan in a blind eye go to show that rinnegan is separate from sharingan.
Also, you stated that you needed an ocular power to get rinnegan, but byakugan is an ocular power, so even if your statement is correct in saying that you need an ocular power, Hagoromo having byakugan before rinnegan would in fact meet that requirement.