[Mightypeon]

As an actual change for the next CBM, at the moment, Sappers are by far better choices than Arbalests for nearly everything:
reasons:

Arbalest fires every 3 turns, does 14 AP damage, range 45 precision 1.
Crossbow fires every 2 turns, does 10 AP damage, range 30 precision 2. It also has 2 more shots.

Already here, the Crossbow is imho a better weapon, after 6 turns, the "total damage" of the Crossbow is already better (since 3 Crossbow Bolts likely deal more tha 2 Arbalest Bolts), the crossbow is more precise which is usefull. The Arbalest has some uses when it comes to strong alpha strikes, and against masses of units who are resistant to 10 AP. Which is not a lot of units.

But the most important things in favor of the Sapper:
Map Move 2 and Siege Bonus of 5.
In Sieges, each Sapper is worth 5 Arbalest guys. A modest amount of 40 Sappers (something 2 normal forts can get in a single turn) is enough to instapop most 150 def forts, a main army with a contingent of 100 sappers will blow through any non Pan fortification in a shockingly quick way.

Imho, increasing the precision of the arbalest and or reducing the Siege Bonus of the Sapper would be nice for internal balance.