Density isn't the sole predictor of environmental footprint. Pretty few of us would argue that an exurban McMansion is more sustainable than a condo, but once you move away from the extreme ends of the spectrum it does become more ambiguous. For instance, from what I've seen, NYC's per capita carbon emissions are actually pretty comparable to Toronto's despite being about 2x as dense.the five apartments with basement accommodate how many people, like 10 max? I don't know how you can compare with the density highrises provides.
Even within NYC, you don't actually see huge swings for household footprints, even if you compared the Upper West Side (which i *think* is the densest residential zip code in the US) and Yonkers or Flushing. On a per capita basis, that gap would be even smaller I imagine.