4 cannons at 300 meters versus 100 arcuballistas +50 trebuchets + 150 regular ballistas= 1 big hole in the wall? Nope not buying it, not in reality. Only in the authors imagination would that work.
1)they dont have trained cannon cocker's
2)concentrated fire from all those ballistas plus the trebuchets would immediately knock them out of play unless they literally buried them in bodies to defend them in which case they could never change their aiming trajectory
3) rolled cannons have seams that are welded which heat up and crack and finally go boom when used repeatedly as much as the author says they are used
Etcetera...
Psechi