GO Expansion is a band aid on a wound... if one has to travel upwards of an hour, what difference does it make to them if their local line runs every 10 minutes or every hour? They're still pissing away an immense amount of their time, because some enlightened planners decided downtown Toronto is the only place that deserves to have employment, services, arts or culture.
No, de-densifying downtown and trying to correct the mistakes of the last 50 years in the suburbs (a big ask, but it's the only way we can possibly make the GTA a livable place) is the only logical way forward.
I'm not sure your assigning blame correctly.
Toronto has in fact tried to create mini-downtowns in NYCC and STC and the hope is for something along those lines at Six Points, while the former East York wanted one on Overlea.
Money was spent on streetscapes, on permissive commercial zoning and more; and it turns out, uptake on the office space that was built is only so/so in NYCC and so poor elsewhere that few towers were built and 2 on Overlea were turned into Condos.
NYCC did get its own Performing Arts Centre, but it struggled to fill itself (and still does).
That's not to suggest we couldn't have or shouldn't have had more balanced development.
But a variety of things were done incorrectly.
MCC was not built next to a GO line; neither was SCC or NYCC, though at least the latter got subways.
Part of what creates energy in downtowns is the presence of young people; but the universities located in North York aren't at NYCC, nor is the University in Scarborough at STC; nor is Mississauga's Uni at MCC.
Those decisions don't fall on City planners for the most part though. The province had a great deal of sway.
The other thing is......frankly, when you've got an established centre, that's well served, it can require a heavy stick, not merely a carrot to send development elsewhere.
Former Mayor Crombie's 8-storey height limit was part of just such a plan, it may not have been the right idea, then or now, but certainly it might have shifted where some things ended up.