Obviously, I'm not able to comment on Marc's understanding of political science back in 1977--or that of any of the other Founders--but I will note here the intrusion of your own subjective view which seems quite skeptical of . . . "concreteness," shall we say, in the analysis of political systems. So let's keep that apparent bias of yours in mind in this discussion.
Again, I'm not able to guess at anyone's intentions but we can look at what they created. A numerical value for "Government" which was generated by a 2D throw (with -7 DM) and modified by the Population value as a positive DM. Thus, we get that more populous worlds will tend to have a higher Government value as our only conceptual guidance. So here's the list:
0 No government structure.
1 Company/Corporation.
2 Participating Democracy.
3 Self-Perpetuating Oligarchy.
4 Representative Democracy.
5 Feudal Technocracy.
6 Captive Government.
7 Balkanization.
8 Civil Service Bureaucracy.
9 Impersonal Bureaucracy.
A Charismatic Dictator.
B Non-Charismatic Leader.
C Charismatic Oligarchy.
D Religious Dictatorship.
Now the first few seem to make a sort of simplistic sense. "No government" fits with a small populace if for no other reason than that as soon as two or three folks start "cooperating" in some manner vis-a-vis the other folks you have ~some~ sort of "government."
We can argue about what "company/corporation" governance looks like but this really makes no sense because any "corporation" is simply a legal and administrative ~creation~ of some ~other~ government! (In the Imperium campaign this "other government" must be the Imperium and therefore it's a world ruled by the Imperium!) This has been commonly interpreted to mean a world ruled by an off-world corporation but isn't that simply a particular instance of "captive government"? We're only at No. 1. . . .
Participating democracy--as in "demarchy" where everyone gets a direct say in governance--fits well with a small populace but if we consider some commonly understood examples of this--ancient Greece (or the ~antebellum~ U.S. where black folks, brown folks, Indigenous folks and white women had no vote)--we realize immediately that these are examples of a much larger society where ~most~ of the folks didn't have much say in governance. Ancient Greece--and ~antebellum~ America--was actually more of a "self-perpetuating oligarchy" in which the oligarchs practiced "participating democracy" amongst themselves. So, perhaps this type ~isn't~ particularly tied to a small populace. . . .
Next is self-participating oligarchy and now I'm thoroughly confused. Why would this type tend to have more populace than a "participating democracy"? We're at No. 4. . . .
I'm not going to talk about what a "feudal technocracy" is. (There are thousands of words about it--to a mostly inconclusive end--in the old TML archives. In hindsight, I'm convinced this was just a placeholder to enable H. Beam Piper's Sword-Worlds to make an appearance.) Perhaps it's sort of "in the middle" from a population standpoint because "feudal" tends to make us think of small groups while "technocracy" seems like it ought to be a lot of folks. Regardless, no one ever ran across this type of government in a political science course. . . .
Next is captive government. Is this like the old Ukrainian Soviet Socialist Republic? Pre-revolutionary America (or post-revolutionary British North America)? Vichy France? Imperial Japan under post-war U.S. occupation? A League of Nations mandate or a UN trust territory? The Dutch East Indies Company? The Hudson Bay Company in Rupert's Land? It might be all of those and yet we still know nothing about the actual ~governance~ within this captive system. Mostly, it's "in the middle" too because there has to be a "larger polity" to be the "captor" while there have to be enough folks for there to be some sort of "government" which has been "captured." Again, not something you're ever going to find as a type of government on a political science syllabus.
Balkanization--now there's a "1970s" (or 1920s) term! You've already pointed out the difficulties here so let's just note what else ~Book 3~ told us about this: "the referee should generate the specific qualities of each territory on the planet separately." Why this one is smack dab in the middle of the population-modified scale is beyond me. . . .
Then come the bureaucracies--again, not a term you will find being used to describe a government type in a political science text. Just about ~all~ governments have a "bureaucracy" of some sort, whether it be small town or the European Union or the Population Level "A" People's Republic of China. Why an "impersonal" bureaucracy would tend to be more populous than a "civil service" bureaucracy is another mystery. (Notice the tendency though with democracy and bureaucracy--and coming for dictatorship--for the "less attractive" version to be the more populous polity or "larger" government.)
Then come the "dictatorships" which are described ~specifically~ on the basis of the personalities of the incumbent. That seems reasonable though it's been a rare dictator who has managed to govern a large populace ~without~ a whole lot of ~bureaucracy~. Now imagine your favourite (or least favourite, I guess) dictatorship. Why would the leader who follows a "charismatic" dictator--Maduro after Chavez, say, or Mubarak after Sadat--slightly tend to rule a more populous polity? Here is more of the implied "smaller" equals "better" American "small-government" ideology.
Next is charismatic oligarchy. Is this Arthurian England under the Knights of the Round Table? The U.S. under FDR's Democrats? Gaullist France? Yeltsin's Russia? Toussaint's Haiti? The Mamluk Sultanate? Google? I have no idea. Nor do I understand why such a government would tend to be more populace than a dictatorship or a bureaucracy. . . .
Finally, there is religious dictatorship, at the top of the list, making it possible only on the most populous worlds. Can we look around today among the most populous states and find a "religious dictatorship"? Iran ranks eighteenth in population (twenty-four back in 1979). It seems like the last time we've seen a government like this it would have been the Abbasid Caliphate or the Byzantine Empire. Both are dwarfed in size by the modern world's most populous states. (Canada has twice the population of the Abbasid Caliphate.)
This is a system of categorization that can best be described as "eclectic." The categorization itself, with a tendency toward higher populations at the higher government types and smaller populations at the lower types is largely arbitrary (and perhaps ideological itself). "More detail," used simply to expand upon these fourteen options, will not bring much clarity or consistency. It's long been understood that most of these government types can also be described by one of the other types. A "company / corporate" government might be a "charismatic dictatorship"--perhaps Apple under Jobs or Disney under Walt--or an "impersonal bureaucracy--like your least favourite telecoms provider. A "charismatic dictatorship" might be a "self-perpetuating oligarchy" or perhaps a "civil service bureaucracy." It wanders on and on and on (or around and around and around).
There's nothing "time bound" about the shortcomings here. The government type system is a hodgepodge of layperson understandings of government types (the "oligarchies" and "democracies" and "dictatorships"), efforts to kluge in campaign elements ("company / corporate" and "captive" and, perhaps, even "feudal technocracy"), and stereotypical American small-government libertarianism (why the "ugly" government types tend to congregate at the higher population end of the scale--and why Government code is a +DM for law level, which is focused entirely on gun controls). An automation-enabled "deep dive" into the details of "religious dictatorship" or "participating democracy" or, for heaven's sake, "balkanization" isn't going to fix any of this. The shortcomings here are conceptual.