"In video gaming, a nerf is a change to a game that reduces the power of a weapon or skill in order to maintain game balance. The term is also used as a verb for the act of making such a change. The opposite of nerf is buff (in one of that term's two usages)"
The term 'nerf' applies. The req one needs to get the full power of something is a change in the weapon's power. If an item can only happen at req 9 now that was previously available at req 8 it's power has changed. You can no longer get full power at req 8.
Just my 2¢