re: Columbus, OH becoming a Major League City?

This Wiki page lists the top MSAs though 381 and is more sortable than the census site, so assuming it's correct, Columbus-Marion-Zanesville is No. 32 with 1.97M, up 3.4 % from 2010, so yeah, it is growing.

Cinci is 28 (+1.08% from 2010) and Cleveland 29 (-.6). Cleveland is 1/3 MSA with decreasing population in the top 50 since 2010, along Detroit No.14 (-.03) and Buffalo No. 50 (-.12).

Largest with no big 4 team:
9. Riverside-Sand Bernardino

Largest with no teams in area at all:
31. Las Vegas
35. Austin-Round Rock
37. Virginia Beach
38. Providence
43. Louisville
44. Richmond
46. Hartford
49. Birmingham-Hoover

LINK

Anyway, you're not going to have 3 teams in any League within 250 miles of each other or 2 within 140 miles outside the eastern seaboard, California, or Chicago with massive populations.