A lot of players have heard of R=U before, including you, which means that Griever was mentioned again. If that's the case, then Griever has became a big thing. If R=U never happened, there would be less mention of Griever, which also means less people knowing what the Griever truly was.

I wonder, though, that if SquareSoft has never intended R=U to happen, would they still change some parts of Ultimecia in Dissida? Who knows.

Actually, I'm not just a fan of R=U, but also a fan of S=R.

Back to topic, I don't like the Ultimania. See, Ultimania is the perfect excuse for Square to admit thier mistakes; indirectly telling us additional information about the Final Fantasy games. For example, if Square has caused a plot error in VIII. No problem there, they can add thier additional information to the Ultimania, hoping to cure that plot error. They do not want to explicitly admit mistakes, so they write the Ultimanias instead. And, that's why I don't believe Ultimania to be perfectly canon. It has been proven that the VII Ultimania has some contradictions to the main VII game.