I think the difficulty is fine as it is.
Yes some players can HQ any 80 dura item with NQ mats, but they have spent a lot of time getting the required skills and gears in order to be able to do this.
HQ mats exist to make it easier to HQ something for less geared/skilled players, i.e. they spend more time to make the same final product, giving better geared/skilled crafters a slight advantage.
That said, if they did actually want to make HQ'ing more difficult, all they need to do is nerf Inner Quiet. e.g. reduced it's effect by 50% or something.