Combat not being lethal / not being resolved in one turn is very heavily tied into 1UPT.
It's complicated to explain the balance/fairness issues that are involved in this combination, but this is a concise and true statement.
(Let's define "Non-lethal combat" as "no insta-kills with similarly tiered units"). While almost all the time one side gets to die, it just needs more turns in 1UPT, or a numerical advantage within the carpet of doom.
If you allow "non-lethal" combat in the CivIV system of SoDs (stacks of doom), you just urge all parties to build even larger SoDs, which will still try to wipe the enemy out within one single turn. That means all players have to invest more production in combat and combat becomes even more tiring.
Imp. Knoedel / Leoreth said:
There is a minor mod, I think it's called Phyrric Victory or something like that, which makes it so that units which lose a fight at >90% odds always withdraw instead of dying.
Why give additional advantages to the side that is already stronger.
Because randomness is no fun.
Randomness can be fun (well, tedious fun), if you accept the numbers and then use them in your favor.
Me (Enyavar!) I'm an unrepentant, saveloading micromanager. I accept the random numbers, but I don't lose fights at 90% odds - I rather fight elsewhere or don't fight if the RNG decides I loose. So, at least for people like me, this Phyrric mod would help to reduce the saveloading. And for other people who try to play through in one single session, it would make things a lot more convenient, too.
You can then attack at 90% odds without problems, but your unit will be at near-zero health after its attack, and thus pretty vulnerable. Yes, the advantage would go to the stronger side, but it goes both ways. And the bonus would also apply in defense: With the current system, if you attack Yerushalim with 10% success rate, in 1 out of 10 attacks, you get to kill the archer. With Pyrrhic favoring Yerushalim, you need to mop up with a fresh unit.
But I said it before: a combat system without strong random factors means that two leaders will parade their armies in front of each other, and the owner of the weaker army has to accept defeat.
Also, I don't see a benefit in switching away from RNG. It dictates a few more things besides the combat outcomes, and you can't get rid of all these systems:
- spread of religion and corporation
- whether or not missionaries fail
- occurence of random events and quests
- Independence movements
- spawns of Great Persons
- exact spawn location and number of scripted enemy barbarians
- reveals from goodie huts
- ... (I certainly overlooked things)