it needs to be balanced WITH archery. Crossbow requires less INVESTMENT to be viable than archery. Learn to use a bow and be a talent to your team and strat faction than some bundle of sticks with a gun.
and it also requires(depnding on the xbow) 2-7 seconds of standing still. Archery requires NO stalling.
Archery:
Faster draw spead
(you CAN wear upper light/lower medium armor) but most wear light armor
Requires 6 points in PD(or so) depending on the archer
Pierce or Cut damage
Crossbow:
No point investment beyond WM
Pierce damage only
Slow reload
Can wear heavy armor if wished(Specced xbows wear medium to light armor too just like archers)
Might have missed a few, but that's the differences in the 2. (not counting other things like arrow weight, upkeep costs as those are modifiable by devs and can be argued that they are roughly the same for each class)