Unfortunately this isn't a bug. While exspensive to do it does make for a pretty effective defense line. All races have giant units so anyone can do.
Would suggest taking some siege units with you when attacking castles to take down archers on walls and save a few extra troops
I know how to play, I know how to kill archers, and I know how to use 3 catapults. Those are replays from other players since I'm only waiting for the new server to join with my old house, but that's not the point.
Do you really think it's intended that a whole pack of swordsman will just stand in front (or even worse, inside) of a giant unit's body while archers drop a rain of arrows on their heads instead of going to the side to attack the wall? Have you seen the animation when those units try to walk away from the catapult? That's stupid, sorry. Doesn't make any sense. It's clearly a problem with the AI code. lol
If you're talking about filling the whole wall with giant units body, fine, they wouldn't be able to reach the wall. But that's not even realistically possible and that's not even what I'm talking about. I'm talking about units being »stuck« »inside« of those giant units. Please, look at the last screenshot and see Virion running right to the only catapult on the field with a whole wall free for him, and then being stuck.
Also, no, catapults are terrible for defense.