The AI in general is rigid and defiant to the extreme, sieges are just the place where it's the most obvious. But yeah, camping ballistae with a menavlion or standing in the middle of archer routes are the most efficient way to farm dozens and hundreds of kills in sieges with next to no risk. Their inner desire to touch that ballista is so pronounced that an enemy knight standing next to it is deemed inconsequential.I killed probably 50 archers in siege once with a sword. Not because I am some master, but because the AI is so bad, they must get to point A and anything in their way will be ignored. It's really really bad. A year and some out and the siege AI is worse than WB's is not what I call great progress.
blah blah poetry aside there's something wrong with AI priorities, the fact that they don't care about surviving and only want to attack one specific enemy soldier or reach one specific nav objective is obvious and needs attention if the game is to be presented as a combat sim