UAL planned to have a MCO hub back in 1991. Started building it up but then they bought the Pan Am Latin network in 1992. So that killed the MCO plan.

But calling MIA a hub is pushing it. A focus city with a crew domicile would be more appropiate.

http://www.departedflights.com/MIA99intro.html

in 1999:
Domestic Destinations Served:
Atlanta, Chicago O'Hare, Denver, Los Angeles, New York LaGuaria, Newark, Orlando, Washington Dulles,
Washington National


http://www.departedflights.com/UAMIAhub.html

based on the above link MIA peaked at 36 flights a day (subject to months not reported)