I don’t fully understand what the problem was when you had one per county, but dispatch centers will not change anything with mission generation unless you change them from default. You would need to set it to own coverage or out of service if you do not change to those settings they do not change mission generation.
My guess is you built some federal stations and maybe they took over your missions with cannabis missions. And maybe you built the max needed of 8, if that is the case put 7 of them in a dispatch center by themselves and set that dispatch center to out of service. That will leave you with 1 federal station to get missions from and you will still have 8 for mission generation even though only 1 is generating missions.
Your explanation of the federal police lost me. Since missions are generated by the number of stations assigned to the dispatch center, it would allow missions anywhere in its coverage area. The fed police missions worked fine but the fire missions became a problem. With the advent of the station classifications, I think that fixed my problem.