Witchcraft essentially covered everything. I think that the most important thing to learn about being an xbow is the use of cover, not just to reload but to hide from the enemy team. When you can take shots at an enemy who has no idea you even exist, your odds of hitting are much greater. If you bring an arb/Heavy xbow into battle and 1 bag of bolts, you can carry any 1H weapon in the game (I prefer the steel pick to compensate for my low PS and you have high enough athletics at lvl 30 to compensate for the short reach). I would suggest the heavy crossbow though, mostly because it reloads faster and still does a lot damage while being cheaper, than the arb, which is much slower and more expensive, but both of them are really good xbows.
If you ever want to try out any of the loomed xbow gear I have, I am sure we could work something out.
Hope this helps!
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Edit: not sure about the wpf values...
You forgot to mention the fact that arbalest has a delay in the release of the bolt making the heavy crossbow better than the Arbalest. imo