This subject is really low priority. Blizzard will balance the numbers anyway the way they want to so we are talking strictly about the aesthetics of it. That being said, the aesthetics of it are indeed bad when epics last the entire expansion for about 99% of it. I agree it would be cool if the system was something like:
whites: questing, 5man normal, non-elite drops
greens: 5mans heroic, raiding normal, final-boss 5man normal
rare: raiding heroic, 5mans mythic, final-boss 5man heroic
epic: final-boss raiding heroic, mythic raiding
Of course, this is the point we all should remember why this doesn't happen. They want to please the majority. And the majority does not wait for end-game raiding.