I like the idea of power comparison. It is an easy way to evaluate the forces of both side without making any probability calculations. I would personally rate the combat on 3 values:
Strength: Determined by attack defense values of units and the amount of units.
Volatility: The amount of speciall abilities that could have an impact on the battle.
Magic: The potential of the ennemy wizard to influence the battle.
All these variables are compared separately, so you dont neet to evaluate for example, how much a volatility point is worth of army strength point. So players analyse these variables in order to take the "do I attack or not" decision.
If you want to make this information unclear using scouts and spies, that is fine with me, I don't really care as long that the uncertainity is indicated in the number. For example I am sure he has an army strength of 25 but I think he has an army strength of 75. The value 25 is cetain, the value 75 could be lower or higher than the actual value. If Information scouting gets better, the minimum and uncertain value would be close to each other.
So the system abovve could be easily calculated by comparing values and making averages and medians.
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Now the other thing I would like, which did not seem to be undertood, will be illustrated below. This is how it works in "advance wars":
1 swordman unit VS 1 dragon and 1 priest unit.
1-I select swordman, select which path it will move. I move it next to the dragon
2-I select to attack the dragon.
3-The game show: 5% to 10%. Which mean that this attack will inflict to the dragon from a minimum of 5% to a maximum of 10% of damage to the dragon. (based on it's max HP)
4-Since this attack is not very efficient and the dragon is full strength, I cancel the move.
5-Instead I move my unit beside the priest.
6-I select the priest as target and it shows, 60-80%. Ah! Much better.
7- I accept the action, the units move in place and attacks.
8- Repeat the process for every move.
That's it. It's a simple attack evaluation to make sure you do not make useless attacks, like scratching the dragon, without knowling it.