So I have been working on military units and mass combat some.
The basic idea is that any given benefice holder who cares about such things will likely have between two and five military units, discounting militia or somebody very very rich who spams cheap infantry hordes. Each unit is a discrete formation which is able to meaningfully do War Stuff by itself though varies in size depending upon exactly what it is.
There are only six basic types so far, three grades of infantry (Regular, Elite, Special), with the better troops coming in much smaller numbers and so actually weaker units overall, then Armour, Artillery and Flitters. They have fairly specific roles and so there should not be an optimal choice, it depends on both an individual's resource distribution and their goals.
So are you a rural baroness? You absolutely want to go for lots of regulars, you have plenty of Manpower and are liable to need to actually fight battles. A Guilder and a city mayor? Perhaps you fulfill your feudal obligations to the Duke with a couple of tanks, or have a flight of fighter bombers, relying on arming up your militia to guard the city walls.
Each unit then has a 'Training Level' from 1 to 6 and can pick a Speciality for every point in excess of 2. Specialities could be something like 'Desert Expert' (Better in deserts), 'Ranger' (Better for scouting or raiding) or 'Terror Troops' (Messes up average or lower training foes).
Unit types come with a base training level but you can work to increase it for individual units, mostly through persuading a PC to spend multiple strategic actions working on things. So hiring a badass to come lead/train your troops is seriously helpful. Also units can be given more/better equipment as expensive options, so you might have a unit of Regulars as cavalry, or equip a unit of Specials with powered ceramsteel armour, if you are rich enough.
So moderately complex but each person who does have an army only needs to deal with a few units and they can be recorded as say 'Regulars, Training 2, Mounted' or 'Elites, Training 3, Motorised, Grenadiers Specialisation'. The main idea is that it is not just 'Jill has more troops than Bill and so matters more'. Jill might have a horde of desert cavalry raiders who are super devastating at skirmishing in deserts, Bob might have a bunch of stalwart line infantry and some artillery who are inferior overall but a lot better for sieging a castle or holding a mountain pass.
Jane might then have nothing but a few dozen cyborg space knights in powered armour who are really not a match for either on a battlefield despite costing at least as much but you absolutely do not want disgorging into your palace unexpectedly or boarding your spaceship.
That kind of dynamic is the goal at least, with the plan that just going 'I have three units of regulars and one unit of elite retainers' should be completely valid for anyone who does not want to do anything fancy and, overall, the optimal strategy if you do not have particular goals in mind.