Granted, I only play siege, so I don't know how all the x-bows affect battle.
But in siege, the x-bowers have no impact on the outcome of the match. People take pot-shots during the first minute or so, occasionally someone gets a lucky headshot, but it's not like bodies are falling left and right to the onslaught of bolts or anything. As soon as the attackers breech the walls, ranged is a liability for the defense, not an asset. I typically bring an xbow for my first D spawn, then don't bring it after I die once. It's just something to do while waiting for the attackers to breech, but I rarely get xbow kills.
1 shield skill opens up the 200 HP crappy board shield, which will last long enough to ascend any ladder, as long as no defenders are throwers (I haven't seen a thrower in weeks). I don't know why you can't do the same in battle; just bring a shield and nullify all of those x-bowers. Or bring your own X-bow and shoot other x-bowers while they reload. Your choice.