There are posts on this thread that go more in-depth. To reiterate on bus network changes, they lead to more transfers being needed, and trips being effectively much longer in duration. Line 7 itself is predicted to be slower than the buses it would directly replace(/supplement?)
Normally, these consultant aided or consultant authored cases are post hoc rationalization, they're meant to support the government's position on the suitability of the project. The fact that they had every opportunity to cook the data to make Line 7 look good and yet somehow managed to make it look bad is shocking. Unless you think the city was against Line 7, prior to Olivia Chow.
As I understand it, it's not that ridership on the Line 7 corridor would be necessarily decreased. It's that ridership would decrease for the overall transit system.
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Both Line 5 and 6 were projected to increase transit ridership. Even if Line 6 may not reach that projection immediately, it certainly wouldn't decrease ridership, all other factors being the same (covid, reduced Humber College attendance etc.)