How long are you willing to wait? The reason Truman is building wood-frame across the street is because the construction costs and the revenue psf make sense. Concrete towers are more expensive and need to be sold for more $psf.
Consider what is immediately surrounding the Westbrook site. Is a Dollarama, a dumpy Wal-Mart and a huge mall parking lot as your immediate neighbour something that you can charge the same as being in the Beltline or Kensington? If you're seeing what I'm seeing (and very likely what Truman is seeing) then the achievable revenue psf you can make won't make for a profitable concrete tower project, so it simply won't be built. If the mall and the surroundings don't change, how will the value proposition of the location increase?
For Westbrook to be built it needs to be built at what is profitable and achievable as it sits today. Waiting won't necessarily make it more feasible to build towers; this is a good place for 5-over-1 developments for the entire site, with good materials and architecture and an emphasis on a well-designed urban realm and public space.