Mercs are almost always better than your standard troops. However, eventually the player will amass enough wealth to build better barracks to create better troops but that is with a single player. Recruitment also works by region which means you could deny others soldiers but, hey, that's war! A go to war with what you have plan will limit the size of armies and reduce the drawback of only having a limited number of mercs per recruitment zone. (Don't let any one player have to much power)

Simple is fun. It's clear which units are mercs and which are regular. I suggest a simple, in-game solution instead of counting turns and trusting (but verifying, which takes time) that the proper amount of troops are disbanded.

Have these simple rules been tried? What is wrong with them? I have plenty of laws and rules I must follow at work. When at home it's time to get dirty and have some fun!