In DF-Lite game Gnomoria, I had much a similar setup. Every time the goblins would attack my settlement, there was one "clear" path inside, that wound along a serpentine corridor - that was entirely comprised of trap doors on every single floor tile. they'd all file in, and when the first one got to the end of the corridor, it'd trip the trap doors, and everyone in the corridor would plummet thirty stories down a shaft to their death. Then my gnomes would take the stairs down, grab all their weapons and armor to melt down for the metal, and butcher the corpses so there'd be plenty of goblin sandwiches to eat over the coming winter.That is, of course, an option that many traders eventually take. Sometimes their civilizations will send an army to besiege my fortress instead of traders. Which then results in their army getting slaughtered by my traps and military. And then I loot the weapons off the dead and use them to make even more traps. And melt down their armor.
In previous versions of the game I could even butcher their bodies to make food out of their meat, leather and parchment out of their skin, handicrafts and bolts out of their bones and skulls, and thread out of their hair. But alas that feature has been taken out in the version I'm currently playing.