So, the conculsion is that Siege engines are not rigged, but a mere miscalculation in maintaining a strategy.
Siege engines are very,very, very powerfull, but not at all un-beatable. Other units, shuch as chims and frosties are very very powerfull as well.
So yeah, some things are imba... if siege engines work, they own. If the enemy beats them, your kinda screwed.