I play singleplayer and i love defending my base against the purges and its a shame that the trebuchet useless well to me it is because i never use it but having a thrall operate it would be well cool having it fire over your walls weaking the purge as it appoarches well it was just a thought love this game cant wait for chapter 3 and golems 
Ballistae, or other kind of siege engines too, would be amazing. I think it would make raiding and defending more fun as well.
Not sure if being operated by a thrall would make it overpowered… 
Oh wait! Finally something against those pesky little wizards hanging from their bats! 
Yes Please!
I would prefer balista against trebuchet. About the flying “rats” archers should work properly. I never understood, how simple arrows can damage a trebuchet!
A ballista against a trebuchet would make more sense than arrows. 
They are also easier to place on your rampart. The trebs with their bases are so huuuge.
I think that ballistae were more of a anti-person weapon though. Just impale the one operating the trebuchet. 
Edit: Well there were also ballistae hurling stones. That would be good against a treb I think.