... a knight can't kill a scout in open terrain with one shot ...
When you say "can't" do you mean reproducibly, or that you just got unlucky once or twice? Because this sounds a lot like the old spearman vs. tank straw-man argument. It's definitely possible that the promotions are a little too much right now, but let's look at it objectively. One interesting thing I've noticed is that some players seem to have way more promotions than others. I'm pretty sure that this is because they massively expanded their armies late in the game, whereas some have very few promotions because they just upgraded units throughout the game along the way. If that's the case, then it's an interesting point, because the common sense of the game dictates that an upgraded unit should be stronger than a newly built one.
Update: v5.8
- A.I. units start with a small amount of experience at higher difficulties, based on difficulty setting and era. This compensates for the fact the A.I. does not manage experienced units well.
Did I just get unlucky or is this reproducible? I wouldn't call that a straw-man argument - just a false dichotomy.
It's a straw man argument because we're talking about giving units combat promotions, not making scouts competitive against knights. I personally haven't seen that behavior, but if it is indeed the case then there's no reason it wouldn't be possible in the vanilla game either. The issue here is only giving free promotions that are otherwise still available. Even if it made a scout able to kill a knight (or a spearman able to kill a tank), that would be because the core game mechanics allowed it, not because this mod enabled something special.
Like I said though, it's definitely possible that the free XP is too much. If my observations of it possibly too heavily favoring late-game built units heavily over early-game built units that have been upgraded, then one solution might be to increase the base XP bonus and decrease the per-era bonus. I need to playtest it more before I come to any conclusions though.
Sorry, you obviously feel very passionate about this so I'm just going to back off.
I'd be very much in favor of replacing the open/rough terrain bonuses with just combat 1/2/3 like Civ4 had. As it stands now, there's very little reason to ever take the open terrain bonuses, because rough terrain is always going to be better for defense, and since you get an open terrain attack bonus anyways, it's better to take the rough terrain so you can have a chance at taking out units on hills.
This looks a bit dull but helps the AI a lot to develop quickly equally strong units than the human player.