now prosperity is linked with security as well, and dropping in a large amount of troops (200 fians champion) only increase very little of security (+4) while the prosperity reducing like -20 security. Dumping more troops wouldn't work either as it cost a lot of money to maintain the troops, making the idea of own a town to make money completely useless, i might just own workshops and caravans for money making.
There can be several solution:
Keep the link between prosperity and security but increase the garrison troop contribution to security.
give us the option to stop prosperity growth of a town or a castle, like what you have already done for auto recruitment.
TaleWorld and developer, you guys did a great job for the game and i have played over 1000 hrs now, the game have gone more and more narrow with money and play style, this could turn into forcing the player to play in only a certain way (trade lots) this limitation on playing style reduces the fun we can get from the game. I understand a game should be challenging and reflecting the real life, but too much of them would make the game loses its fun.