I dont think exp deserves a separate part. My first thought was:
1) if both sides didnt take any damage, no exp is gained to anyone.(ranged attack dealing 0 damage). In all other cases exp is gained as usually
2) add additional ways to get exp for AA-units, air-sweep and so on.
Do you think these two simple changes are not enough?
The most significant problem with exp is instant heal. If ranged attack deals less than 3 damage (and that happens often), it will probably be harmful for you. That is strange paradox that you shouldnt damage enemy units sometimes.
But that problem is most easily solved by just removing instant heal.
Actually, if you want to get to other microproblems like farming exp by having fortified melee near CS that can get these 2exp/turn as long as you want... I dont see simple solution for this.
Complete rework of exp system could've been like this:
1) xp for fight is reduced by half (1xp/shot, 2xp/fight)
2) for kill you get 10 xp (even by ranged), for capturing a city you get 20 xp
3) if killed unit is one era behind of killer, xp gained is halfed (5xp). 20xp if it's one era ahead.
This can encourage real fighting, and reward you for killing more advanced units.
Or we can make xp-system even more thoughtful/complicated, so that you receive more xp by dealing more damage, or by attacking stronger units.
But do we need it? I'm not sure.
Ranged units are counters to melee units, especially after logistics. Crossbows (especially Longbows) do quite a bit of damage as they are upgraded. One shotting a Longsword is possible. If it's fortified (Ie, someone is very solidly set there) you can take promotions to cut into that bonus.
Mounted units counter ranged units and with charge can do decent damage to fortified melee units while others clean it up. If the +100% vs. mounted promotion gets dropped, Cavalry have the same CS as Rifles, and will clean them up quite well with the right promotions.
Granted, their best promotion is charge and it's currently too far into the promotion tree, hence why I want it brought down a level.
Move/attack/Move is the bonus mounted units have. I also want to bring the extra movement point promotion down one level, to help out mounted units.
As well, the fact that you can just go around the close units and pillage/trash an enemies territory.
First, it clearly shows you lack MP experience. I'm not saying that everything you said is wrong, nor I'm saying that i'm mega pro. It's just things you described work only theoretically. Things dont go as smoothly as you described. But I think that you can still understand and analyze what I'll explain now.
In MP its really very hard to have so promoted units. Enemy will try to actually kill your units. You cant have few warriors going through ages to mech infantry. Units will die, its inevitable.
So, you need xp buildings to have promoted army. But that takes time to build and you have to pay maintenance. For example, you can have 3 units lvl2 or 4units lvl1. In game such two armies lead to stalemate, because one side will be defending, and when you defend you can successfully do it having less totalCS/firepower. But overall four lvl1 units will be more effective than three lvl2 units (against, for example, two lvl1 units being in defence). That is mostly because of instant heals. That means that lvl1 units are not that worse, or even better than lvl2 units, because of instant heals. lvl3 units are a little better than lvl1. But that means that you need 2 additional buildings in each your city. You cant build units only in one city. In case of military activity you need all your cities produce units. The conclusion is that you need to spend hammers, you could have spent for new units or other buildings, but the benefit of this is not that big. I assure you, instant heal is very strong thing.
About promotions. Logistics is extremely great promotion. Basically it doubles your attack and xp. Lvl5 (100xp) is too low requirements for it. Really, compare it with charge, that you say is great. Its only 25%CS added. The same goes for "if target is fortified" promotion. BUT, you forget about "the usual choice", +20% in rough terrain. That means that if you choose charge instead of +20% in rough terrain, you will be only 5% stronger. It wont solve a problem breaking through fortified melee at hill. Leave alone +1 movement promo, that you get instead of +20-25%CS. And with movement 3, mounts cant move-attack-move. Melees usually move through rough terrain, thats why if you dont stand at adjascent tile at the beginning of turn, you will only move one tile to get closer, than spend 2 move points to attack. Just like any 2move point melee. If you stand near enemy you want to attack, its too dangerous for mount, cause it doesnt have rough terrain or fortifying bonuses, and its unlikely that you will be able to make 2 actions (attack and retreat) without being attacked at least once. (if ping is equal)
About mounts being counter for ranged and good for pilaging. Mounts really can attack ranged units before being shot. But such situation is almost nonexistent if both players are decent. Melees always move in front of. Melee:Ranged ratio is usually higher than 2:1 and its very hard to attack such army from undefended side. Even if you will be able to do this, this is a suicide mission. Enemy will kill that mount without losing anyone: two attacks with same-era melee is enough. And you need 2,5:1 CS ratio to kill that ranged in one hit, but usually mount:ranged CS ratio is only 2:1. And also, such maneuvaring means that this unit have to spend more turns going to battlefield around. That is why pillaging is also bad idea unless you can destroy strategic res: your mount spent 10 turns going around to pillage something, but enemy had just build a unit and it is ready to fight your mount. This factor might seem not important, but it is. And you dont need high tech mount to pillage, even horseman or scout will do. I agree, such pillaging may be a nuisance, but the result of such raid is not always more beneficial than having additional unit at real battlefield (where most units are).
And the last one: calculations.
To "one shot" longswordsman with longbowman with logistics, you need at least 1.5:1 ratio. That means LBM with +60%CS=3promos. Against LSM lvl1 standing on plains. And actually that is with two shots.
Now, lets get real. At 1:1 ratio ranged deals 3 damage. LS has 16*0.75+16=28CS at lvl1, simply by fortifying in hills. Crossbow will deal only 2 damage. It'll be 2damage even with one fortifying. How come this is counter? At the other hand, ranged kill everything else...
Cavalry lvl3 with rought terrain bonus and charge = 36CS. Rifleman lvl1 fortifying in hills= 44CS. Where is "do decent damage to fortified melee units"?
If you call ranged a melee-counter, than its rather ranged is good against everything. And melee is perfect in defence and good in attack. Just build melees and ranged and win. Kill everything and be unvulnerable. Right? Check link in my previous post and you'll see that with those changes such strategy wont work anymore.
Not saying everything I wrote is right. But at least it's things to think about and consider.