Except that all arrows in the game can be used with all bows (except the foot bow) and the all weigh 8 oz. The same with bolts and crossbows/arbalests.
That's obviously for ease of use in play (as well as minimising bookkeeping). An arrow from a significantly smaller bow (27" Handbow arrow) wouldn't be able to be fired from a standard longbow (which would require a 36" or greater arrow) at all - at least not without substantially underdrawing the bow (and thus sacrificing range and power - increment and AP). Also, surely you jest about the fact that you think an Arbalest uses the exact same size Bolt as a Hand Crossbow?
I'm also of the opinion Longbows should have something like Massive, for what that's worth (just while I'm thinking about bows).
Frankly the bigger annoyance is that the blackpowder weapons should either all have the same damge code, or that the blunderbuss, pocket pistol, and dueling pistol should have different ammo lines.
Agreed. Though I'd call it an annoyance of equal magnitude (

). It's something I've actually changed for my next game - same damage codes because it's the same size lead ball, just range and wey model apon quality differences.
Wait.... You're complaining that bows and crossbows which all use the same ammo mechanically should have differing damage codes because in reality they fire different ammo, but then argue that the blackpowder weapons should all have the same code because mechanically they all fire the same ammo, when in reality they don't.
I give up. I will never understand the need to fix that which isn't in broken in a quest to accurately model an interpretation of reality.