Yeah we can't change the growth rate of cities, that is universal.
One thing we could do is make all specialists produce -1 food, essentially making each pop cost 3 points of food not 2 (exce3pt for those working in the fields). That could be crippling though...
I haven't yet figured out a way to do something that would not cripple them.. another alternative might be UBs that produce unhealthiness.. or all specialists produce unhealthiness, or certain specialists produce unhealthiness...
Another option might be a set of Ghoul UUs that cost more pop. to build, simulating a lower population as one unit represents a higher percentage loss..