Whether you call it an Uchiha power or not, the fact is only Uchiha's who are Indra's incarnates can awaken the Rinnegan, so it is technically an evolution to their powers.
And it's a manga fact that the true powers of the Rinnegan are shown only when used by the original owner, and this was proven by Madara and Sasuke, who displayed far stronger Rinnegan feats that Nagato (who borrowed the eye from Uchiha Madara), they took it to a whole other level.
So yea aside from the Sage, the Rinnegan belongs to the Uchiha, deal with it. =D