I do agree a lot that 700 years or more is a long long time! One tends to forget these basic numbers and other data when remembering history - at least the amateur kind of.
But that leads me to the question I had in mind for a long time:
How do we - or rather Civilization 7 or Humanind 2 - better frame the early game units than by their weapon? What can we name them instead of spearman/swordman/warrior? Apparently, it‘s more about organisational possibilty and logistics, but that just doesn‘t lend itself to a catchy naming convention. And if we take in ranged and mobile units - does it still make sense to have Archers and Chariots as separate Units?
I long for a better naming - but I fear we are stuck with that anachronistic idea as it‘s so set in our minds - kind of like the scaly dinosaurs (don‘t add me, I know it‘s more complicated than „they all have feathers now“).
I've started posting my ideas for a "New Combat System" trying to thread the gap between Civ VI's 1UPT abomination of bad temporal and geographical scale and Humankind's micromanagement of every sub-unit in a battle, here:
Combat System for Civ VII
Basically, there is no reason for the Grand Panjundrum of a Civilization to control anything on a battlefield, unless he/she is personally leading the army. In a 4X game, you should be making Grand Strategic (which weapons do we manufacture, how do we arm the troops, how do we raise, feed, and train the troops?), Strategic (how and where do we want to fight our wars?), and Operational (How do we get the enemy to fight us when and where we want to fight him, and nowhere else?). Tactical decisions about who stands and who charges, who throws spears and who calls down artillery fire are, frankly, None Of Your Business.
So, I would reduce your basic decisions about Units to two parts:
1. What kind of weapons do we arm them with?
- and this includes the very important element of not only how do we get the materials to manufacture the weapons, but how do we afford the time to train the people to use them, because some weapons are just too expensive in time and effort for the average city-dweller to use (case in point: horse archers - no bunch of city dwellers or farmers EVER became horse archers). This means for some Units typed by their weapons, the origins and criteria for forming them will have to be a lot more 'exotic' than we are used to in our current 4X games.
2. Are the troops gong to be Amateurs or Professionals?
Amateurs for most of history (roughly, to the beginning of the Industrial Era) were simply Everybody Who Showed Up, bringing their own weapons and equipment with them, but also expecting to go home after a short time, because they had jobs, shops, farms, pastures and other livelihoods to attend to. Some of them could be extremely proficient Amateurs - most Greek Hoplites were of this category, but it was a Civic Duty to show up fully armored and well-trained in the
Gymnasium to defend your city. In other words, and like most Amateurs, there is a Social or Civic component to these Units that is even more important to their formation than the Weapons.
Professionals are those who fight for a Living. They are available all the time, can train all the time, and so can handle effectively some much more complex (and versatile) weapons. They are also, compared to Amateurs, Expensive to keep because they have to be supported - except when they are looting someone else, they aren't doing anything to pay their own way.
Some weapons require the time and effort only available to Professionals: Swords, Cavalry with Bows, Cavalry with Lances, most Siege equipment, etc. Other types of Weapons can be used by either Amateurs or Professionals, but the Professionals will, all things being equal, be better with them: spears, pikes, battle axes, muskets, rifles, crossbows, etc.
Some weapons are 'naturally' available to certain classes of the population. In any pastoral group, virtually all adult males know how to ride and shoot a bow, because that's what they use to defend their herds against predators on 2 to 4 legs. If you want Horse Archers, in other words, Hire Them from the pastorals: there is a reason that both Rome and Byzantium had large numbers of Hun Cavalry as mercenary components of their armies. Shepherds on foot in most societies also became adept with missile weapons -javelins or slings - to protect their flocks so that they are essentially "self trained" as Slingers or Light Infantry (Classical Greek
psiloi). Warrior Aristocrats or Noble Warriors train themselves because their self-image is tied to being proficient with weapons - but that group needs some way of supporting themselves or being supported, which will be a Social/Civic System like Comitatus or Feudalism that will have Major Effects on the rest of your Civilization/Faction as well.
By including the previously-ignored component of Societal Support (Amateur, Professional, Civic/Social requirements) to the simple Weapons we get both a more accurate depiction of armies and units but also (finally!) can show the relationship between the army and the society that produced it. A large professional Roman Army was not possible without also extending the basis for recruitment to virtually all Roman Citizens, while also extending Roman Citizenship far beyond the original inhabitants of the city of Rome. That also turned out to be the basis for maintaining a relatively stable and inclusive Empire for centuries. That started before the Empire: Hannibal and the Carthaginians ultimately failed because they were not fighting the city of Rome only, but Rome controlling most of Italy and able to recruit most of the Italians into effective Roman armies. The exclusive Greek city states with their Social/Civic structure could not have formed an Empire that was other than coercive beyond their original city-state borders, as Athens' attempt to do so demonstrated.
Society = Army in very fundamental ways, and it also affects the rest of the Society.