Well, if you're going to play as a crossbowman, play as a crossbowman. Grab a heavy or preferably sniper if you can afford it, stay somewhere a bit off and try to snipe horses (which is a big help to your team when you down one), ranged, maybe some hero meleer if you get the chance. You'll get the opportunity to farm kills when it's melee time (the fighting got near / further away and you're mopping reminders), someone tries to backstab you, etc.
It's a different playstyle then melee with crossbow sidearm, and it's generally a more relaxing one sometimes. Of course melee wpf helps, but it helps for everyone who isn't one of the bundle of stickss which run away from every opportunity to get kills in melee.