Maybe, that would have to depend on the terrain the open battle is taking place.
The point of historical TW games is them being as historically accurate as possible, they can't take away the challenge of a siege battle because its a pain in the ass.
To some extent i agree with you, siege battles in TW games suck.
Instead of removing them, CA should evolve them, there should be more options to sneak behind city walls, have spies place explosives for your attack etc. There are lots of things CA could do to make siege battles more enjoyable.