in addition to supplementing the end-game with extreme battles and other challenging content, we will also reduce the difficulty of the existing high level content at the same time
I can't see any good reason why you do this. ("others mmos are doing it" is not a good reason)

If the content is fun, people may want to do it again months/years later. Especially in a game where reroll is encouraged.
Are you implying that you don't try to make the content fun? Is it just some clever time sink and you reduce the old time sink when you release new time sink?

And what about the progression curve? Primal hard -> Primal extreme is an obvious progression, but if Primal hard are made easier, the curve is broken.