As the title indicates I propose a rework of the Provincial investment system.

At the moment you can only expand a city/Province by investing Political Influence (PI).
Which in return means a single province minor can expand his cities at the same pace as a mighty empire. Because they get roughly the same amount of PI.
This leads to very boring and unrealistic gameplay.

My humble idea would be changing the PI cost to actual money but it gets more expansive the bigger a city or Province is. Additionally terrain like Farmland or reccources would give a cost reduction.

with this simple change an Empire can actually use economy to grow their cities instead of monarch mana.

This idea ist mostly taken from M&T a EU4 mod which uses a similar design but with great effect !