I watched some of Arumba's videos. The dude sure knows how to min max! He was arguing for only requiring Citizens and Slaves and worrying less about the other two pop types and REALLY not worrying about their buildings because the bonus to growth etc is just too slow. Only the Marketplace is useful
What do others think?
Unless you want to play an uncivilized tribe, you'll want to get rid of tribesmen, so that leaves citizens, freemen, and slaves.
You get more military bang for the buck using freemen rather than mercenaries, and you can make armies of the unit types you favour using national manpower, which is why freemen are so lovely, but mercenaries don't require your manpower pool to regenerate which is a point in their favour if you use them in the best way possible: to absorb the brunt of casualties.
So use both.
While it is certainly possible to play the game relying solely on mercenaries and only using citizens and slaves, I cannot recommend it. It is just about as stupid a choice as you can make, as that would require you to do manual promotion on a large scale, something that requires a vast expenditure of monarch power.
But what, I hear you cry, about worrying
less about the other two POP groups, i.e. not deliberately getting rid of freemen but not caring that much about them either?
No such thing. Sure, not caring much about freemen is standard operating procedure in any large country in Imperator: Rome
, but so is not caring much about citizens or slaves either.
And that is because once you've conquered your way into a large country or have started as such, you'll not be doing much manual promotion as it is an inefficient use of your monarch power: you'll be using governor policies. Civilization Effort to get rid of tribesmen, Social Mobility to move the citizen/freemen/slave demographics towards an even split.
Finetuning by spending oratory to promote individual POPs to citizens in a large country is an insane waste of monarch points unless you are determined not to expand any further and just want to fiddle with the demographics of your country as is; In all other cases it is better spent on laws and fabricating claims.
As for buildings... honesty compels me to admit that I mostly find forts useful, and that's it, preferring to spend money on mercenaries to expand even faster. But then, I'm a slightly more aggressive player than the average when playing SP.
Though it must be admitted that stacking up on marketplaces in the capital to reach 60 civilization faster if intending to switch government in the early game is a very useful approach.
EDIT: Of course, if you don't intend your country to expand in the first place and are happy finetuning a small country and staying weak, perhaps having as a personal challenge how strong you can become while staying small, my advice above doesn't apply at all as it is based on playing Imperator as a map-painter.