Well, Houston still has two buildings that are slightly taller than Toronto's tallest (excluding C.N., of course), and Los Angeles has one, but where T.O. objectively surpasses those two cities hands-down (and Chicago, too) is in the total number of highrises.
Since the CN Tower is, by far, the most notable feature on the Toronto Skyline, I think it should certainly be considered when discussing the skyline. The technical consideration that keeps it from being defined as a building, that it is not habitable floors all the way up, does not keep it from being, well, visible, after all. The antennae on First Canadian Place, are also considerably taller by the way, though perhaps they should not be counted.
I think Chicago is still well ahead of Toronto in most respects when it comes to architecture. Until fairly recently, I think you could also at least make a case for Houston also. It is a few years since I was there but I do not think there has been all that much construction since then. In Houston, there isn't the gradual buildup of midrises, to lower highrises, to the Central Business District that you find in Toronto. That makes the Houston core really stand out from a distance, in a striking way.
Also, from some angles, the sheer height of the CN Tower can make the Toronto CBD just seem short by comparison. You don't get the sense of how tall those buildings actually are. From a distance, the tallest building in Vancouver, the Shangri La, actually looks taller than the Toronto core. In fact, there are probably a dozen or more taller structures in Toronto, but they don't stand out the same way the Shangri-La does.
To go back to Houston, however, and to a number of other American cities, they do not have the impressive extent of tall buildings that you find in Toronto. Beauty is subjective, but I feel confident in the opinion that the combination of height and extent makes Toronto the third most impressive skyline in North America.
