The Slinger is actually not that bad. I added a Technology to turn the Stone cost into Wood cost making it viable in lategame.
Comparison Slinger vs Composite Bowman:
Attack 2+3 vs 5+1
Hit Points 25 vs 45
Range 4+2 vs 7+3
Armour 0 vs 0+6
Pierce Armour 2+3 vs 0
The Slinger is a good anti Archer unit, especially because they have +2 attack against archers and +4 against cavalry archers. They just have 1 less damage than Composite Bow but 5 more piercing armour. They will easily win a 1 v 1 against one.
The Camel Lancer is designed as an Iron Age upgrade to the Camel Rider. A fast cavalry to hunt down enemy cavalry and Cavalry Archers.
There is purposely no Bronze Age Upgrade for the Axeman because the Short Sword is only a little bit stronger, making it useless if there is an better Axeman. Thatâs why I moved that to Iron.
I also made two distinct Ram units. One light, fast but not armoured Ram that is available in the Barracks in Tool Age and one slow Ram with good piercing armour in Bronze Age. Maybe give the Elephant more siege damage and make the Ram not available to civilisations with it. Or make the Elephant benefit from the Ram upgrades in the Storage Pit.
I would make the Caravan available at the market in Bronze or Iron Age and performance wise between Trade Boat and Merchant Ship. Sea trade should be better than land trade because it fits better into the period.
My general idea for the balance is:
Anti Infantry
Archer the Bowman and the Improved Bowman as well as Cavalry and Elephant Archer
Swordman they are good against other Infantry (might need a small bonus damage, the Shortsword already has it)
Ballista good against groups of Infantry
Anti Archer
Light Cavalry The good speed makes them hunt them down
Camel Lancer same as Light Cavalry, especially against Cavalry Archers.
Slinger as I explained earlier
Skirmisher like in AoE2 but less of a hard counter.
Siege units Catapults and Ballista eat them for breakfast.
Anti Cavalry
Spearman like in AoE2 but less of a hard counter
Phalanx cavalry can only run away against them
Camel Lancer Hunts down Cavalry
Others
Catapract is good against Infantry without spears and relatively good against Archers. They are good all round especially with their new AoE upgrade.
Elephant they are a mix between siege and anti Infantry, Archers can easily keep their distance.
Axeman they are a decent base unit that can take on Infantry and Cavalry with the new Iron Age upgrade but they are very weak against archers.
Every civilisation should have one good unit from the 3 categories above.
Spearman should have an Eastern design because Mediteranian Civilisations normally have good Phalanx or Camels.
Battle Axe should look like a Germanic or Celic warrior.
Auxiliary Bowman should look Middle Eastern as it is available for those civilisations and was often recruited from there for other like Rome (if they need it).
Light Cavalry Should look like from Central Asia
Camel Lancer Obviously Middle Eastern.
Royal Chariot Either Hittite or Egyptian style.
Recurved Bowman can look Mediterranean. Easy to make look neutral.
Skirmisher like Greek Peltast. They look Anatolian.
The new sprites that I mentioned should also fit the Civilisations that have boni fro them.
Legion should look good for Romans, Choson and also the Mesopotamians but they should have less of a Roman looking shield as the Centurion.
Phalanx should look more Greek. The shield should look like the Hopilite but Iron instead of Bronze and the body like Centurion. A Lambda could be cool but that might look to much like Sparta.
Catapract should look Asian as itâs the strong unit of Shang.
Heavy Cavalry Archer should fit for Yamato (Japanese) and the Sykthes (new Civilisation)