The current War Wagon UU of Korea is actually based on the Chinese war wagons.
Timestamp: 12:47
War wagons of China are like tanks. Massive and huge. The one in the video is a custom wagon for the Chinese Emperor without any bolt thrower.
A much better UU for koreans would be the Hwacha or Korean Rocket Thrower.
In action
Even samurais are nothing against this (The UU should have bonus damage against infantry units)
Hwacha > War Wagon