Its to help new players get to the newer stuff faster, if you already completed it why are you complaining than. You are not be affected, you are just pissed because you already surpassed the stuff. Don't you want new players to get to where you are at with short time, what if your real life friends decided to play the game all of sudden. I am sure you would want them to catch up to where you are at as fast as they could and that is what this does.

Nerf isn't really a nerf but its a gate way for new players to catch up. They already explained how to get the buffs not to be apply if you really dont want to see the buffs. Also the buffs are even lower for the more recent content like Primal EXs