I don't think Toronto is the most congested city in the developed world, and I'm pretty sure it's far far better than Kolkata, Hyderabad and Jakarta (I think Bangkok's not as bad as those, but probably still worse than Toronto).
This is my impression of the various contenders.
I would say these cities are definitely ahead of Toronto: Los Angeles, New York City, London, Paris, Tokyo
Less obvious but probably still ahead: Berlin, Singapore, Seoul, Hong Kong, some smaller Japanese cities (others might be in next two categories), Chicago and if you consider them single cities - some of the conurbations in Germany+Randstad
About on par: Chicago, Bay Area, Washington and maybe Boston, Milan and Sydney and maybe maybe Dallas
Slightly behind: Melbourne, Houston, Philadelphia, Atlanta, Detroit (far behind in some measures, but economy is still decently big), and then Barcelona+Madrid (much better urbanism/transit, weaker economically)
Then you have some cities that are less wealthy, but still far ahead of Lagos, Delhi, Kinshasa, Dhaka, etc and much bigger, they're not as important in finance, but I think the importance of finance is over-rated. These are places that have the resources to continue to develop rapidly, I would say the first tier among these is ahead of Toronto, and then next one is quite close. I wouldn't really consider these third world cities because they have no shantytowns (although they do have crowded and poor neighbourhoods).
-Sao Paulo, Shanghai, Beijing, Buenos Aires
And in a tier a bit below
-Shenzhen, Guangzhou, Taipei, Bangkok, Kuala Lumpur
And below still
-Tianjin, Chonqing, Istanbul, Cairo
Then there's some cities with some shantytowns but not too many and still relatively developed and big, I'd put Toronto a bit ahead of the first tier of these. Some of these cities like Rio are often in the spotlight for having slums but even most of these "slums" have running water, sewers, electricity, masonry buildings, often even internet access, although they can be quite poor and high crime, they're still a far cry from real slums like the ones common in Africa (and a few places elsewhere).
1st: Mexico, Rio, Johannesburg
2nd: Jakarta, Ho Chi Minh City
3rd: Karachi (doesn't seem to have that many shantytowns)
Lots of slums and shantytowns, but at least a decent amount of middle class as well
-Big Indian cities, Manilla
Lots of slums and relatively small middle class
1st tier: Dhaka
2nd tier: Lagos, Kinshasa
Not sure how to compare: Moscow, St Petersburg, Dubai, Tehran, Baghdad, Luanda
Not sure about some of the other big south american cities ex: Lima, Bogota, Santiago, Belo Horizonte... some of them have issues with crime (esp Bogota), others less so. South American cities are generally not growing very fast though, and less wealthy, so they have less of a chance at surpassing Toronto. Only Bogota and Lima are significantly bigger.
I would say that:
Africa and especially South Asia is overpopulated imo and getting worse, so there will continue to be a big gap in wealth vs Toronto imo, projections of economic growth in these regions are overestimated imo because they don't take into account resource scarcity issues
China and Latin America are less overpopulated than South Asia and have relatively moderate population growth
Southeast Asia is not too overpopulated and have a population growing at a decent pace