I used to be of the same thoughts as you but I'll show you why I changed my mind.,
1) Those points are focused on commuting. I am concerned about all vehicles using the highways, including B2B (trucks) and leisure. Trucks coming in from the US on the 401 are not headed for downtown. As more people move to Ontario, more infrastructure is needed. As a animal grows, it needs more and bigger veins to transport nourishment. (this is the main and most important reason)
2) Regarding commercial investment, Toronto had a multi decade drought in building, the future is downtown Toronto but its also a bit of catching up.
3) Business knows it's too expensive to live in the GTA and branches are opened in places like London, Kitchener /Waterloo, etc.
4) While on the job search recently, I was focused on the downtown core but most of the jobs were Markham, Scarborough and Mississauga. For many, that would mean a trip on the 401.
While I completely agree with your sentiment and would prefer a Toronto where your proposal was the best one. The GTA doesn't have the land use pattern for it. I'd rather Ontario was as economically successful as possible, which includes an increase in all transportation infrastructure.
I recently (unfortunately) ended 8 years without a car