Apologies to differ slightly from the OP.

Atm I have about 80-90ish settlements in the year 135 in my Romani campaign with cities such as Segestica, Dalminion, Gader, Sucum-Murgi and Pella all pumping out roughly 13k per turn. I have a ton of upkeep costs lost in military so potentially if I disbanded a few of my full stacks, would I see the (visible) income of these cities rise further? Or would it increase the income of other cities that are not making as much? ie. Athenai 2500ish/Roma 4500ish/Syrakousai 4000ish.

Hope that makes sense.