Hey, this is my favourite showcase so far! I've been tracking them for a while now.
I too think it is great how the AI is actually skilled in attacking/defending castles in this game.
As for catapults taking out gates, I don't think you should be able to target them. In BFME1 this just resulted in battering rams becoming useless... All you did was bombard their castle from a distance and they could do virtually nothing apart from either charging out or quitting the game. The same also goes for archers. I found that putting men on my walls became suicide, as they were begging to be sniped... IMO catapults' only use should be to randomly bombard the city, causing fires, destruction etc and maybe causing structures to collapse on their defenders...