Board Thread:Naruto Discussions/@comment-29393962-20161111215453/@comment-1512913-20170114141917

The Rinne Sharingan split into Rinnegan and Sharingan, which Hagoromo inherited. The Sharingan part got passed down to Indra while the Rinnegan part is split between chakras of Indra and Asura. So a Sharingan isn't a lesser Rinnegan/Rinnegan isn't a higher stage Sharingan because both are already equal fragments of Rinne Sharingan.