It is very difficult and complicated to build a tower 500 feet, the higher you go the more risk inherent in the project, and the less likely it will be built, or even financed. Good, sound, reasonable proposals are what build cities and sustain growth cycles.
From elevator design, to sales, shadowing to wind/gravity forces, to cost and location, supertalls are VERY risky, difficult projects.
Peoples comparisons with China, and Dubai are insane, real market forces aren't building those towers, Chinese nationalism, and an oil depleted sheikdom are. Hence removing the risks incurred by developers, banks and contractors.
It's just not comparable AT ALL!!!!
What you can and should compare Toronto to, if you must, are same size cities, here in N.A., ......a reasonable list of comparable downtown skylines, and economies......Again looking at metro areas, San Fransisco, Detroit, Philly, Atlanta, Seattle, Dallas, Houston, Los Angeles, Phoenix, Las Vegas, Boston, ........ When you look at these places, and you consider adding the growth Toronto has had, the impact would overwhelm the markets and infrastructure of most places.
Phoenix' growth, sprawls ever outward, even Vegas with its "unreal " market had coughed up a massive down turn.
You can not overstate the unbelievable spurt TO has seen, We are racing toward Chicago/ New York status, whom we are really not economically on par with yet.....and even they are not building like we are!!!!
Many of the worlds super talls, are stalled or cancelled, Moscow, St Pete., London, even Dubai....