Probably an accurate assessment. But while marathoners or cyclists may occasionally be a source of frustration for drivers, the real cause of congestion is the number of large and often single-occupant vehicles competing for limited space. Pointing fingers at marathoners or cyclists who occasionally occupy a single-digit square footage of road space as the source of gridlock problems flies in the face of simple geometry.
The amount of land available for roads is not unlimited, so the only real way to accommodate population growth is to increase density. You could stack roads on top of each other, but vehicle weight is a huge factor in the cost of a raised roadway, so arguably you might get the most bang for your buck by moving light vehicle traffic upwards and away from the cars and trucks. Carpooling would help with density but it's not an attractive target for regulation either politically or practically. Transit eases congestion, but the TTC is a money pit because of its overpaid union workers who can close down the city by striking when their demands aren't met.
Personally I like the idea of a city organized, self-financing car share program using golf cart style vehicles for the smaller road footprint and fuel consumption. I'm not holding my breath though.