i don´t see a problem here sincerly, it´s actually most of the fun of playing kh is sending diplomats to those city´s and wait for them to rebel

an important note is that sending spy´s normally doesn´t work because the ai is actually extremly good at controlling minor rebellions and stuff but with diplomats there (roleplay that they are defending the poor opressed greeks from the nasty and evil barbarians) they tend to rebel at the 1st chance they get

this is actually extremly usefull expecially in the crimean city´s where you get acess to those amazing heavyarchers