Hopefully the new Civ version coming soon will change the crossbow's overpowered defensive abilities. Crossbowman have the uncanny ability to survive longsword strikes, and can even do more damage to an attacking swordman than they recieve from the sword.
You are next to a crossbow dude, swing your sword at him, and despite having a shield and armor, somehow you get hurt more than him in the process!
Medieval Cities with walls and even castles easily get reduced to nothing with just a few crossbows shooting at them. Giant slabs of stone are no match for those little wooden shafts with pointy tips.
To deal with those pesky crossbows... get knights with barracks/armory. Cuz even a deadly knight is not guaranted to kill a crossbow in one attack without special training!
Double rough terrain promotions will allow the knight to kill the crossbow hiding in rough territory in one shot without losing their own life in the process...