A tactical auto resolve where you can see the battle unfold would be great. SD could use the same AI that the enemy uses in the tactical battle.
In the short run, I would offer players choosing tactical auto resolve two options to guide the the AI;
1. Magic Strategy
a. No Magic
b. Use Magic against strongest units
c. Use Magic against weakest units
2. Battle Strategy:
a. Target all
b. Target strongest enemy units first
c. Target weakest enemy units first
Example 01: Magic Strategy (No Magic), Battle Strategy (Target strongest enemy units first)
Example 02: Magic Strategy (Against strongest units), Battle Strategy (Target weakest enemy units first)