In my opinion:

1: 30 years of refinement of the platform
2: Olympic-class development of sails
3: Olympic-class crews
4: Olympic-class research on how to sail the boat fast

No doubt, many boats could have been as fast or faster, but they have not been subject to the same intense research as the T. It doesn't hurt that the design was fast from the start as well, even if there are faster hull shapes today. The 10 foot beam is a 'must' when the wind increases.
I think it could have been even faster with daggerboards instead of centerboards.

Edit: A more interesting question for me is "what could make the Tornado faster/better"