This couldn't be more false. I look at complete team rosters every year. Georgia gets probably 80% of their starting players from in state every year. LSU same way. Auburn, which is on the GA/Alabama border gets half of their players from GA and half from Alabama. Alabama and Mississippi, same thing.
Yea some players come from Florida to play at other southern schools but its the same at Florida schools. Florida schools have tons of athletes from other southern states every year.
But your statement is flawed. In the south each state provides for itself for the most part. Every southern state is about 50% black so there is no shortage of talent in any state.
GA, Louisianna, Alabama, Mississippi, SC, NC, Arkansas are all sesspools of athletic talent.