Board Thread:Theories and Speculation/@comment-34997073-20200620190326/@comment-1512913-20200621081723

Simple explanation. Rinne Sharingan is a parent to both Sharingan and Rinnegan. Kekkei Mora simply means, the progenitor/original ability.

Like Kaguya's Ash Bones are KKM and Kimimaro's bones are a KKG, diluted version of it. Therefore in the Sharingan-Rinnegan family, Rinne Sharingan is the highest one can get.

There are people who have both the Sharingan and Rinnegan:
 * Madara had to switch between the two and couldn't have both active at the same time
 * Sasuke can have both active at the same time unlike Madara, but has only 1 Rinnegan (most likely because a pair is more powerful, as not to make him too overpowered)
 * Urashiki for all we know, might have had the Sharingan as well, explaining the tomoe and is just like Sasuke, but has 2 Rinnegan, making him technically superior

Now, having powers of both the Sharingan and Rinnegan and even being able to use them at the same time, STILL isn't the same as having the Kekkei Mora Rinne Sharingan, I'd say it's a close 'recreation' so to speak, but still inferior.