Have you lived in Ottawa because a lot of this seems pretty ignorant to history and reality.
To start with the Trillium Line literally uses DMUs to serve suburban areas and is being further extended to serve more suburban areas. Exactly as you are whining about. The only difference is that they ended the extension inside Ottawa's city limits.
Next, a regional rail system would be useless since the existing rail infrastructure doesn't reach the downtown core. Making it useless for most commuters. Heck, there's entire suburbs with no rail lines running through them.
Lastly on cost, Ottawa basically built a metro network cheaply by mostly converting existing BRT corridors (the Transitway). Building any of this from scratch would be extraordinarily expensive. The entire Ottawa O-Train network (both Stage 1 and Stage 2) only cost 15-20% more than the Eglinton Crosstown and unlike the ECLRT is fully grade separated and segregated, has larger stations and longer platforms, and most importantly 3x the length of the ECLRT (64 km vs. 19 km). Post Stage 2, Ottawa will have 77% of ALL residents (urban, suburban and rural) within 5 km of a rail station. This is better than anything the GTA will have for at least a decade, if not more.
Actually you seem so enamoured with the shitburbs that is Mississauga and Oshawa the you think turning Perth and Almonte into them is a good idea.
More responsible. But not entirely responsible. GO has played a massive role by making it easy to live far away and commute. Only in GTA logic, does it make sense to commute from Barrie, Kitchener and Hamilton to a job in downtown Toronto.
Until the highways fill up. Traffic completely changes the calculus of where people live. And you bring Mississauga and Oakville, but don't want to talk about Oshawa, Milton, Kitchener, Barrie and Stouffville. What transit oriented development is going on there?
Who said anything about living downtown?
If GO didn't exist, Mississauga, Oakville and Brampton would still exist. But the traffic would be bad enough that they would have to actually consider densifying and developing local transit. The 416 would have been forced to densify substantially a lot sooner too. In short, the entire region would have developed substantial differently. More akin to Montreal.
The GTA is increasingly a lost cause. Ottawa is only at a million. They don't need to make the same mistakes as they grow. They've adopted a 15 minute neighborhood development policy.
To be clear Ottawa is over a million now then you add in Gatineau your talking close to 1.5 million.