For decentralized nations estates building should be more important and effective than you try to build in a distant province
Yes, vanilla EU4 buildings are not really suitable for representation of private initiative. But it's mostly an argument to move away from the quite boring vanilla EU4 buildings collection. Not to say Caesar is not EU4, which means that they could do something better. But just replacing EU4 buildings with MEIOU 2.X buildings is enough to represent things like the development of cities, with estates investing in the expansion of cities, mines, farms and players doing their best to protect these locations and helping them grow, while the player constructs buildings which represent state infrastructure. A building system like this is already quite good at representing both private enterprise and state infrastructure. Also, it's awfully boring when it represents only state infrastructure.The buildings actually in eu4 typically represent public infrastructure rather than private enterprise, which isn't represented except nebulously as tax.
Eu4 buildings: forts, trade stations, barracks, rally ground, university, churches, Manufactories, counting houses, harbor, shipyard, forts, state house, courthouse.
For the most part these are things that a government would build with public funds, or are abstractions of limited government investment to expand an industry, etc. EU5 should be a game like eu4: focusing on the development of the state rather than pops. I agree with another poster that there is no reason to have a building system that is out of the player's hands. Nor is it generally desirable to simulate levels of economic activity that doesn't affect or involve the state (get a second monitor to display the NASDAQ as you play).
In my opinion, a building system is genuinely bad at representing private enterprise, but decent at representing state infrastructure. Saying pops should construct buildings then doesn't make any sense. Individuals don't build state infrastructure, and it would be better to evolve the representation of private enterprise out of say the rgo system of vic2 than a building system.