I think their fine the way they are! If Bungie buffs them people will go back and use a fusion rifle the whole game like they did before. You should not be able to one shot somebody from halfway across a map. Fusion rifles are fine the way they are and should not become a OP noob weapon.
Fusion rifles don't one shot outside of shotgun range unless you are really lucky. This means they cannot compete, and they don't have the charge time to compete with a primary at medium range specifically because they do not one shot. Seeing as they are designed for medium range, it is a problem that they can't be effective at this range (at least not the old ones since they were just nerfed). I will withhold my judgement on the nerf as a whole though until I see the current design for fusion rifles.
High impact, high range fusion rifles will. Like Preatorian Foil.
As they should due to their painfully long charge rate.
Like stated above, this post is mainly for PVE. With minor adjustments fusions could be viable in PVP.