I think you summed up the problem with Carlaw and Langley in a nutshell with: "But there always seemed to be several cars waiting to make that turn whenever I drove past". I think it's the waiting, for north and southbound traffic, that's the problem - and the presence of the crosswalk creates a sort of mini-perfect-storm at that time of day in that location.
To what degree will Simpson and Logan be affected? Well, who would bother driving along Simpson ( or Langley ) in order to get to Broadview, rather than going along Gerrard anyway? Indeed, there's a good case to be made that long residential streets uninterrupted by cross-streets ( other than Howland ) shouldn't be used in this way at rush hour when the kids are coming home from school, if an arterial such as Gerrard is available. But, if someone is determined to drive west on Langley at rush hour, they could still do so - by going along Gerrard or Simpson, turning up Logan, and turning left onto Langley.