The whole solution to the siege problem is to allow the option to turn the timer off, and then allow the option of "last man standing" victory conditions for sieges. This would allow the AI to play in a way that showed some instinct for self-preservation.

It's pretty obvious that the R:TW designers were told to pick up the pace in tactical battles and make them more "exciting." That explains just about everything that's questionable in realism terms: Foot units that move too fast, excessive kill rates, murderous archers. I also think that's what's behind the friendly fire problem and the disappearance of the spear rank bonus, because those aspects penalize the time-honored tactic of setting up a spear wall with a bunch of archers behind it, making battles more "fluid" and "exciting." It certainly explains the goofy "flying horses" or "horses as projectiles" effect in cavalry charges.