I also think that you guys are missing something about the south...
So highly focused on football for decades...there are more southern athletes in basketball than ever. And growing fan bases.
Basketball at the high level has had a northeastern flavor for a while...
But now...Auburn's roster has 16 guys from Alabama, Georgia, Louisianna, Florida...regional athletes. Not the normal recruiting ground for UConn, Nova, Georgetown.
Mississippi has two guys from north of the Mason Dixon line (West Virginia & NJ)...
FSU has 11 southerners, and 1 from Chad, 1 from Switzerland, 1 from Ontario...a Massachusetts kid and 2 Illinois players.
Basketball had an urban flavor when I was younger...and the south was more rural than it is today. But now, the sheer numbers of black athletes in the south, combined with more interest in the game may help southern programs.
Football is still the king...but basketball is no longer nearly invisible.
I agree that southern basketball has gotten better, but I disagree with a number of your conclusions.
First, rosters tend to have a heavy local influence, as you would expect, so I would expect SEC schools, for example, to have more local players than not. Same for Big 10, Pac 12, etc... But, you missed one of the biggest trends in college basketball which is international players. And, where do all of the starters on the sweet 16 teams come from?
International 12 (Gonzaga has 2)
Georgia 8 (Auburn has 4 and FSU has 2)
Texas 8 (Houston has 3 and Texas Tech has 2)
Illinois 6
Indiana 4
North Carolina 4
Florida 3
Michigan 3
Ohio 3
Pennsylvania 3
Virginia 3
Alabama 2
California 2
Louisiana 2
Massachusetts 2
Minnesota 2
New York 2
New Jersey 2
South Carolina 2
Wisconsin 2
Also, look at LSU. The starters are from CT, NY, NJ, Louisiana, and England. In other words, LSU was able to go outside of their local area to recruit and their coach is in trouble for improper recruiting. FSU? FL, two from Georgia, MA, and Senegal. Tennessee? AL, TN, IL, NC, and Canada.
Look at where the All-SEC first team basketball team came from:
Arkansas, Texas, Connecticut, New Jersey, Mississippi, Gabon, Illinois, and North Carolina.
The All-SEC freshman team:
Alabama, Arkansas, 2 from Canada, Wisconsin, Virginia, Florida, New Jersey.
It seems the SEC has broadened their recruiting outside of their geography as most of the best players are not coming from SEC territory.