The defensive button is the black sheep of autoresolve. It almost never gives a desired result, even when you have missile and siege superiority.
See LegendOfTotalWar: https://www.youtube.com/watch?v=HeE_Egquplg
I think it is ideal for a cheat because buffing it 60-80% actually gives it an outcome that is only about 20% better than the other buttons.
I like to use artillery and missiles in combat (and so does the AI).
The damage inflicted is less because both sides retreat early.
I have decreased the percentage retreating by about 20% overall.
The damage profile is excellent: it is spread evenly across the army
The cav are much less likely to die.
The generals are less likely to die on each side.
However, without this player buff, the AI will is given several hidden buffs in defensive battles that make the results undesireable.

The other buttons can have better outcomes even with this 60-80% buff on this button.

For ex, if you have heavy cav and the enemy has <40% spears and >40% missiles, choose aggressive unless it is a settlement or camp.