ummm no.. When the large tenants in Calgary relocate to newer office buildings they do what every other firm in North America does ... downsize the amount of space per employee, this is a trend that's here to stay and will only continue over time ... this coupled with alternative working locations (i.e. at home) fuels this even more.
Re: Height, there are so many factors, its not a Calgary vs Toronto thing ... For one the Calgary office market is hotter per ca pita, no doubt about that, its by far the hottest in North America, though that's starting to settle down now.
Keep in mind when Toronto's boom started, the buildings were fairly tall, with BA being +200m. The difference at this point is there is just about 5 million square feet of new construction in the greater core of Toronto. Less in Calgary, so Oxford like the other large commercial property developers here in Toronto know there is a lot of competition and given they are in the industry they can approximate the demand. Oxford knows filling a 240m building in this climate (even 3/4 years from now) would be difficult, they could take a risk, or get away with a shorter tower which is easier to fill, and correspondingly easier to profit on.
Keep in mind they did market the tower at a larger height at the start (and it was marketed for a while), simply put they probably couldn't secure a tenant large enough to go with the taller version.