Personally, for me, it's the high missile speed coupled with the infinite hold that really gets me.
If you spot an archer aiming at you, you know they have a limited time to judge the shot & loose, then the arrow moves at a reasonable pace so that you have enough reflex time (providing you're a reasonable distance* away) to get out of the way.
With an arbalest (and in fact any crossbow) they can follow you indefinitely and they're not pushed for time, so, if you're in the open, unless they have never played an FPS (exaggeration) before you're going to have to avoid a super speed projectile. Now, I would expect most of the people playing today to have quite good reaction times (given our pedigree of playing partially reaction based games) and it's ridiculously difficult to avoid it.
In short, my opinion on arbalests, ignoring the massive reward for little risk & payload of damage that they dish out, the missile speed really detracts from a higher degree of skill needed to successfully hit a target. To suggest a change, it would be to missile speed, but that would be considered a nerf & I would preferably know the mathematical repercussions & current damage over distance.
Crossbowmen in general have their own place on the battlefield. They're very good at keeping people suppressed just by looking at their target & they should be used to effectively take down high profile targets. They have their place & of course we all hate being taken out in such a manner, but at the end of the day, they did get us.
* Please take into account I'm not talking when you're right up in the face of the ranged player, I'm talking, lets say... A ranged player on the other side of the field on "Field by the River".
I should mention I am trying to see this objectively, but failed to avoid relating it to my own personal experiences versus my own classes draw backs.
