It most certainly does not reflect any 'reality', "Care packages" are not supply and support (modern term: 'Logistics'). The supply of whatever is needed to maintain a military or civilian unit is only 'tied' to a given city or settlement if there is absolutely no other source of such supply. In fact, the only such 'tie' is generally where the original complement of people is recruited from, but replacements for casualties come from wherever they can get them and all the other support - food, fodder for pack animals, replacement weapons and armor, ammunition, fuel, lubricants and spare parts in late Ages - can come from anywhere that can supply them.
In fact, the supply of replacement people, replacement animals, continuous supply of food and fodder for them, weapons, armor, modern fuel and ammunition, throughout history have been 'sourced' from wherever is most convenient. Stealing most of it (especially food and fodder) from the local civilians wherever you are has, in fact, been the most common method.
If we want to limit the total number of military units by modeling the supply chain for them, at Civ's scale it would be far better to simply tie units to the total population so that you cannot 'recruit' soldiers from people who are already hammering out swords, growing food, pressing olive oil, etc and generally supporting everything. This would be far more accurate and far easier to keep track of - as in, the computer can do it for you and tell you when you've reached a 'penalty point'.
I’m not sure about the current Bundeswehr but the German military has used a regional recruitment “Canton” model since the Great Elector, and it’s one of the reasons German units have such tremendous unit cohesion and resilience. The guys you grew up with are the guys you go to war with. The German military went to great lengths to try where possible to return recovered wounded to their “native” formations.
Another tremendous upside, since another part of this policy is stationing units in their “native” area in peace time, is a much, much lower need for coercive discipline. Your soldiers are often stationed in and around where they grew up; desertion or bad conduct will instantly hit your friends and family. You also have them close by for support. The meme of “Draconian Prussian discipline” is complete and utter bullfeathers rooted in typical British dishonest wartime propaganda that became a meme endlessly regurgitated by academic echo chambers, pre 7 years war Prussia actually had a much, much lighter policy.
Prussian soldiers in peace time had two one month training periods and the remaining ten months of the year their time was their own. The only requirement was stay in the garrison town, and wear at least one part of your uniform (usually the pants). Soldiers were not only free but encouraged to seek civilian employment, get married etc. So having a regiment stationed in your town was a net economic benefit; in addition to soldier paychecks you had a stable source of labour. Putting down roots in the community also made a lot of your soldiers “self disciplined”.
This policy is one of the reasons Prussia was able to succesfully support such a large and extremely effective military on such a seemingly slender resource and financial base. It’s also one of the reasons, along with Prussia’s ridiculously terrible geography that Prussian military thought was so focused on fast wars, or avoiding them altogether. Again, it’s comical comparing all the dishonest claims of “German warmongers” with the actual record.
The downside to this is if a particular unit is hit hard repeatedly, it may take longer to return to full strength if it’s catchment area is depleted. If the catchment area is occupied replacements may be imposssible to find. Soldiers may also be pretty unhappy if mixed into a “foreign” unit. I’ve noticed that in several memoirs; Otto Cauis got “promoted” from his original Tiger company to a Jadgtiger unit and hated every moment of it.
During the 7 years war when various parts of Brandenburg-Prussia were under French, Russian or Austrian occupation this was part of Frederick the Great’s juggling act, especially for East Prussian units given the lengthy occupation of East Prussia by Russian forces. Silesian regiments were sometimes given special treatment to bolster the loyalty of troops recruited from a recently occupied province
The use of Saxon troops by Frederick seems nuts unless you keep the regional model in mind. After Saxony was blitzkieged by Frederick the surviving Saxon troops were “Voluntold” into the Prussian Army. Amazingly they were kept in their own regiments with Prussian officers appointed instead if being mixed into often depleted Prussian regiments who could have used replacement because having some Saxon regiments of questionable motivation was judged to be better than mixing “foreigners” into Prussian regiments and disrupting them
Here is a real world example of a major military power, certainly the best pound for pound using what looks a LOT like a military support model based on what city the unit is raised from.
How would you model this in Civ terms?
Using Civ5/Civ6’s combat model since I suspect this is what we will be seeing going forward:
Military Policy Card: Cantons
Effects:
Military units have no maintenance costs in peace time.
During war maintenance costs are increased
Units do not have their combat strength reduced by damage
Unit healing rate cannot be increased or decreased by outside effects, it remains at default values.
Each military unit is “attached” to the city it was built in, if control of that city is lost, the unit cannot heal.