Hmmm.
Most people carry crossbows because it's an effective thing to do with your spare slots. Most crossbowers, I'd bet, have no wpf in crossbow -- they are basically 2-handers who carry the crossbow so they have some options. That's a good and smart thing to do. What else are they going to do? Carry a backup 2-hander? The only reason NOT to have a crossbow is you want to save some money at the expense of having to hide in a building because you have no defense against Rohypnol or Release Arrows.
Certain people put up nice looking KDRs as horse crossbowmen but I really don't think it's that effective. They kill off some peasants and some idiots or slackers out in the open but then it comes down to the endgame they usually lose because a) they run out of bolts before they can kill everyone or b) they run out of time or c) they mess up and die. Crossbows aren't very time-efficient at killing people.
The only nerf I would consider is making crossbow wpf do more.
I do think it's a bit unfair that anyone can carry a crossbow and be perfectly effective with it without spending any points, while throwers and archers have to spend a lot of points and suffer a lot of restrictions in order to ply their trade.
I mean I do 2H + throwing and I have to give up 97 wpf and 4 skill points to be able to throw (and pick up) heavy throwing axes in my main gear set. This means I need 4 WM to get my 2-handed wpf up to something decent. So basically 2H+throwing will always have worse stats than 2H+crossbow and it's somewhat questionable as to whether throwing is better than crossbows or not (better fire rate but half the ammo and crossbow hits do more damage).
So I disagree that crossbows, themselves, are "overpowered".
They might could use some tuning given how little you have to give up to be a crossbowman and how much you have to give up to be a thrower.