All you basketball know-it-alls got it wrong ... Michael Jordan is NOT the G.O.A.T of college hoops -- so says Bill Walton, who tells TMZ Sports that honor belongs to Kareem!

We got the basketball legend just days after MJ was crowned king of ESPN's "College Basketball's Greatest of All Time Bracket" ... and he says the voters got it flat-out wrong.

Don't get it twisted -- Bill LOVES Jordan, saying he's "one of the greatest players, phenomenal" ... but he tells us he believes Kareem Abdul-Jabbar was just better.

"He has the records," Walton says of the former UCLA center. "He has the three championships."

Kareem -- a 1-seed to begin the event -- was shockingly upset in the bracket early on by nine-seeded Shaquille O'Neal.