6 storeys works well for Paris - streets feel built up but not overwhelming. You could add 1,000 units on that stretch of bloor without exceeding 6 floors - and there's little of architectural relevance to prevent higher density.
Not being facetious here - would you support a 20 storey tower on the site? 40? At what point do you draw the line on appropriate height for Bloor St, and what's the test you'd use to pick your limit?
Well, for one, a good lot of Paris' 6-storey buildings wouldn't be buildable in Toronto because they run afoul of Planning's other sacrosanct building guidelines.
I take your point on the building heights -- any limit, whether 6 or 66, is going to be somewhat arbitrary taken on the fact of the height alone (there are other considerations that should come into play with increased density, such as servicing and infrastructure requirements just to name a couple). But to answer the questions directly: no, I don't have the perfect rubric for evaluating appropriate heights; nonetheless, yes, I am fully confident that 6 on one of our two subway lines is absolutely too low, and sure, I don't see any good, unemotional reason why 20 is inappropriate here.
What I will say, though, is that some other of Planning's stipulations have the effect of making taller towers
less desirable insofar as they
limit the types of tall towers that can be constructed (thinking here of limits with respect to separation distances, an insistence on the podium-and-point tower typology, and a whack of others).
I think, broadly, the obsession about building height among Planning, most councillors, and many of this city's residents significantly hinders the conversation about what concrete steps could be taken to build better buildings in the city. In practice, give me a tall, skinny, attractive 26-storey tower that's set way back on a lot line and is engaging at grade over a fat, squat, ugly, lifeless mid-rise with crappy materials and a straight two-storey-high wall of glass any day of the week. Our current regime prefers the latter to the former.