I am aware of that (though some cases less than others), hence I followed it with...
Why? What purpose could this serve, and how could it better justify the attention that Griever recieves throughout the game than R=U?
Again I am well aware of that, hence I called it 'a fairly simple example'. My point was that there are elements of the game that can be thought into, and my example was one generally agreed upon as being worthwhile and conclusive.
I do not remember that, so I can not comment without knowing the context. You may be correct. Though it certainly seems possible that Laguna could be incorrect, or was referring to people with a normal human lifespan. My point was simply that stories involving time-travel frequently involve such occurences, and that the apparent oddness of R=U is lessened by this fact.
Sephiroth's Cage: I may have misunderstood you, but unless there is an external or seemingly random element involved in the time-loop, then I don't really see how it could change... I certainly don't see how such a change could result in Ultimecia's existence in all of the cycles, as Ultimecia is required 'prior' to the change.
I like the Squall/Griever idea, though I don't support it due to references earlier in the game to Sorceresses going bad not having knights. The idea of Rinoa becoming Ultimecia is supported by the idea that IF she did somehow outlive normal humans, at some point she would lose Squall, and thus have a good chance of becoming evil. I don't see a good reason why she would turn evil despite Squall's presence.