Separation/deamalgamation won't do anything to get needed transit built - those decisions happen beyond the scale of the municipal government and as such we don't really have a regional body wielding the kinds of power needed. Any alternatives one comes up with will probably have regional governance with regional level representation, which basically a repeat of the current situation.
The difference is that separate regions usually have a better understanding of what they can and can't afford, and realise that they are asking for subsidies when they want the greater region to help them out. It reduces the unnecessary in-fighting and sense of entitlement.
My issues go beyond transit, though. Libraries, sidewalks, bike lanes, parks, etc. are much better handled by local communities than regional bodies. Transit needs to be necessarily a mix of local and regional bodies, together with schools, healthcare, waste diversion, police, and firefighters.
Right now the city of Toronto is stalling because mayor Ford, suburban councillors, and urban councillors can't see eye-to-eye. This level of paralysis is obvious now, but it was also an issue during Miller and Lastman.
The casino is yet another example where politicians actively try and externalise impacts onto other wards while reaping the benefits themselves. Meanwhile business areas within Toronto but outside of downtown are held hostage with high commercial tax rates.
The geographical area encompassed by the current city of Toronto makes no sense geographically. It's either too small to account for the GTA, or too large to serve its individual communities. I doubt that even the best most qualified mayor would be able to fulfil the potential of the area under the current configuration.