Not sure if this is intended. I know some civ TCs in Imp have a bolt they shoot that does ~80% dmg to knights. Not sure if I had full blacksmith upgrades if that matters.
The blacksmith upgrades count for tc too, so u can improve the dmg by 3. It’s I think 9 dmg per shot from garrisoned vills, and 11 from main tc I think. They only civ what can buff it more is French with red palace landmark. Then the tcs and keeps from French shot for 70 (?) dmg with one arrow.
Chinese towncenters get a hand-cannon shot. English town centers get extra arrows and French town centers get high damage arb shots if you build the Red Palace. However yes, unless you are Red Palace French, TCs do like 0 damage to knights. They have 6 base attack (up to 9 with upgrades), so imperial knights will be taking like 1-2 damage per arrow.
The starting town center gets 1 arrow that does slightly more damage, but all the extra arrows from garrison still only does 6