I agree with all the points you made and will add a few. The autocalc seems to work on the assumption of an all out charge by the attacker. So archers in an attacking army don't seem to help much. Especially annoying against bandits.

Recently autocalced a battle as ERE. 2 bandit peasants against a family member, 2 legio lanciarii, and 2 eastern archers. I lost 20 men. Obviously, under human control, I would have just let the archers go to town and would have lost none.

There is at least one situation where autocalc can be your friend. Had a situation as Sassanids where A Roman general was under siege basically as the only defending unit behind some large stone walls. I did not like the idea of dealing with all the towers (no artillery in the army) so i autocalc's and lost only a handful of men. Much less costly than my experience of taking the walls even when they are not defended.

I only autocalc when my army is composed of cheap easily retrained units. Normally against bandits.