to autocalc a battle is like cheating, specially if you attacking a castle, IMO.

The ai probably just look at the number of men then calc it.
I was outnumberd 4-1, the enemy had 16000 i had 4000, I won a great battle, then i reload to see how it was if i autocalc. then i would have lost my entire army and only killed 1000.

And if you want to become a greater fighter you have to fight every battle, even if it looks like your gonna lose