I'll give you that Tsukiyomi and Amaterasu were most likely known when it was said rinnegan is more powerful than sharingan. Kakashi and Sasuke both experienced Tsukiyomi and Jiraiya witnessed Amaterasu first hand.

But I feel that eternal MS/ability to summon Kyuubi were unknown to everyone but Madara, Itachi, and now Sasuke. These were the secrets to the Uchiha Clan Itachi was referring to. If anything, the elder Uchihas new about these secrets but their knowledge of the secret was lost after the clan was killed. Even when the clan existed, killing other Uchihas for MS and killing brothers for eternal MS was long out practice and remained only as a secret. To reiterate, after the clan was killed, the secret was killed with the exception of Madara and Itachi.

Itachi tells the story of Madara, his brother, the origination of MS, and obtaining eternal MS to Sasuke because Sasuke did not know about it. For Kishi to introduce this new information in this way leads me to believe this was obviously unknown to Sasuke and has and still is unknown to everyone else.

Of course, even with our new knowledge of the extent of sharingan/MS, we do not know the extent of rinnegan's power because of how little exposure we've had to rinnegan. At this point, I find it hard for rinnegan to have a power that trumps immortality and the ability to control an entity with practically limitless chakra.

There is always the chance Kishi could come up with something more for rinnegan to blow sharingan out of the water and I'll believe it when I see it. It's just, at this point, the information we have been given leads me to my current speculation.