In fairness, Nick's Academy (and Nick himself) groomed 10 future #1 players and many slams:
Agassi 8
Courier 4
Rios 1 final
Not to mention Hingis, Sharapova, Seles, the Williams sisters and helping Boris late in his career.
Yes, Rafa has won 20 slams but his Academy was founded after the bulk of those were won. So maybe Nick has a proven and long track record of producing world class tennis players. Maybe the Rafa Academy will someday get to that level, but for now, Nick's Academy remains the gold standard based on results.