Cancelling flights 10 hours after the incident (actually some that are 21 hours after have been cancelled because their inbounds were cancelled) out of a fear of ruboff delays was a business/operational decision, completely within their control. Using the weather coding is supposed to be for flights that physically can't be flown, not a "well this will cause downstream delays if we decide to fly it." The airport was back to normal operations hours before the scheduled departure of at least half of the cancelled flights.
I am sure there will be a lot of complaints from people that were told they could get on a flight on Tuesday or Wednesday and told they could go buy a ticket from a different airline that was actually operating out of MCO today (i.e. every airline except Southwest).
FYI, I worked in airline flight ops engineering for years, so I have a pretty good understanding of what goes into these decisions. Flights were cancelled out of a fear of impact on the rest of the system, not because they couldn't physically happen.
Edit: I'm not trying to dump on Southwest, they're my favorite airline by far, I just feel they had a knee jerk reaction here and are leaving their customers holding the bag.