You are missing the point. The Duke family already owns the property. They are already established, with a good business. Changing just one factor, new tax rate vs. old, has such a material impact that conducting business in a location that they already own is unfeasible.
If Dukes was rebuilt, as it was, it would be facing a $90,000 per year property tax bill. That is $7,500 per month, just in taxes. This is a fate that will befall all non residential properties in the city. Areas currently protected by the cap, think Kensington, the Beach, Ossington etc., and almost all of Toronto, will eventually be taxed out of existence.
The vitality of commercial areas, save for Class 'A' office, follow a pattern. Old areas, heavily protected by capping, are doing better than new areas. Queen's Quay is a perfect example.