As one who has a degree in History and a special concentration in Georgia History I can tell you this this is nothing new, north Fulton County was once Milton County and Alpharetta was the County Seat and Campbell County was also another county in Georgia, and Campbellton was the County Seat. In the early 1930s begging of the Great Drepression these counties lost their county to due financial strife and the land was cededed off to Fulton Counties and other surrounding counties. Georgia used to have 161 Counties as opposed to the 159 people are used to now.
You are exactly right with the history lesson 98. Fulton is basically three distinctly different counties rolled into one. The northern portion of the county that wants to split off into Milton is decidedly suburban in nature. The central part of the county where Atlanta, East Point and College Park are has a definite urban feel to it. The southern part of the county where Chattahoochee Hills is located is a semi-rural, if not rural, environment.
One good thing in it for the City of Atlanta is that if Milton does split off, the proposal is for the remainder of unincorporated Fulton County to be merged into Atlanta. This expands the Atlanta city limits and increases its tax base.