KA is a single technique which has only ever been used by one person's eyes... And that person would have to wait another decade to use it. You can't try and base an entire argument on one technique, otherwise you're basically saying "Well Shisui had KA which means he instantly beats everyone." but that kind of logic isn't going to get you anywhere.
You're bringing in hypothetical situations and abilities from about 5-6 characters into one just to try and combat a single Dojutsu... This alone should answer the question as to which is stronger. If you need to add things to the Sharingan just to try and compare it to the Rinnegan, it's quite obvious that the Rinnegan is the far superior ability because you can't add anything to it and you're choosing not to.
Now the user of the Sharingan, however, could factor in whether or not they would be able to defeat the Rinnegan user... For example, I'd like to think that Itachi or Shisui with their amazing Genjutsu prowess would be capable of beating Nagato... However I wasn't talking about specific people when I said Rinnegan > Sharingan, I was talking about the Rinnegan as a whole against the Sharingan as a whole and not individual characters because then I could always just bring in Rikudo - The originally wielder of the Rinnegan and the argument is over... Lol.