I think you overestimate the number of people who would give up a single-seat ride, to save a couple of minutes. Especially given how often the second or third vehicle doesn't appear. One in hand is worth two in the bush (or perhaps a 501 in hand is worth a 3 in the tunnel)

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Riverside/Leslieville is a whole different story (I don't think many will be backtracking from busy spots like Broadview and River, in the wrong direction to the subway). Nor do I think someone who wants to go to Queen/Ossington will head due south to Exhibition station.
Will someone coming on a cold windy day from Queen and Woodbine to Ontario (to use a ride I used to take) get off at Leslieville, trapse through the slush to the station, stand on a cold windy platform, and then come out at Moss Park, go up (4?) flights of escalators, and traipse back to Ontario? The subway ride might be 6 minutes, but it will be a couple of minute to get to the station, and at least 5 minutes to get out and back to Ontario. That's 13 minutes + whatever you wait for a train. Let's say 2 minutes. About 15 minutes total. Right now (5 pm Saturday) the schedule says that's a 16-minute trip if you stay on the streetcar. With little risk that there is a "trespasser at track level". At peak, 8 AM on Tuesday morning it's only a 17-minute trip on the streetcar! And 18-minutes on Tuesday at 5 pm.
Meanwhile, you've already got a seat on the streetcar; and getting on near downtown, and what I assume will be cattle cars, you'll be standing on the subway train.
Then why in London do you see so many buses running on a road, with a tube line under it? (because if you are only going 5 bus stops, you'll get there, before you walk (or more likely elevator) down to the station platform, go one or two stops, and then walk (or elevate) back up again?
Why don't we see a lot more people get off the subway at Main Street and walk to Danforth GO.