Pistol Crossbow

[Skvez]

Throw a teacup. It will be just as effective

Now you're being silly.
A crossbow bolt will do significantly more damage than a teacup.
Is a crossbow pointless - no. Is it as good as an AR 15 - no
Would an AR15 kill my attacker instantly 100% of the time even if I had one - no
A Crossbow (pistol or otherwise) is legal, I can own and practice with it.
Few fights are won in a single blow. If I can damage my opponent *before they close to melee range* I have a much better chance of winning the melee fight than I do if I just stand there like a prune waiting for them to close the distance.
The only other things you've suggested (hammers and bricks) have less penetration than a crossbow bolt, less range and are not as accurate.
Forget reloading, fire the pistol crossbow once then switch to melee mode (stick, knife etc).
The pistol crossbow should be considered as one piece in a defensive strategy including entanglement/ spike traps and a melee weapon.

A BB from a catapult will do similar damage in a vital area and will transfer all of its energy in a non vital area.

Your mileage may vary but my crossbow bolts have a spiked end that penetrate better than a BB and I can aim the crossbow more accurately than I can a catapult, and I can fire it one handed holding my melee weapon ready in the other hand.