The issue with the shoulder-mounted ballista is that it has no counterpart to a real-world weapon (at least, none that I know of). Logically (and on a technical level), such a weapon could work, but once we have someone with what amounts to an ancient rocket launcher listed under their military section, what's stopping someone from coming into the roleplay with something larger, more potent and even more advanced than what the RP's setting would realistically contain? I see Haz's rules as a method in which to curb power creep, wankery and powerplaying, which is incredibly common in nation-based roleplays (and rapidly becomes evident when custom-made weapon and armor designs are implemented into the roleplay).
The only weapon that I know of that could fit with what you have in mind is the cheiroballistra, a light siege engine superior to the Roman scorpio. There is speculation that portable versions may have existed, but the weapon was relatively easy to operate by a small collection of men.
The only weapon that I know of that could fit with what you have in mind is the cheiroballistra, a light siege engine superior to the Roman scorpio. There is speculation that portable versions may have existed, but the weapon was relatively easy to operate by a small collection of men.