Sorry to say that but I think some of your points are off the mark:
Think about that sentence.
Is it all Scarborough commuters? Or merely commuters interested in taking transit to head to STC with the intention of going downtown?
If you want to commute from Scarborough to another place in Scarborough, are you interested in the subway?
If you want to commute from Scarborough to another place in Scarborough, are you interested in a gerrymandered bus route that detours to STC and not continue directly to your office park or plaza along Birchmount?
Scarborough bus route scheme follows a mixed pattern; mostly grid based but with some hub-and-spoke components. So for many trips, detours to STC aren't necessary today and they won't be necessary when the subway opens.
Most of hub-and-spoke routes that will feed into the subway station at STC, exist today and feed into the SRT station of SRT. Most of them would feed into STC even if the light rail was extended. There isn't much difference in how the bus routes will actually be laid out, no matter which transit plan is chosen for the Kennedy - STC corridor.
If you live along the Lawrence corridor, or anywhere west of Kennedy, are you interested in commuting in reverse-direction towards the subway?
If you live near Eglinton, west of Kennedy and not far from it; definitely yes.
Most importantly, neither of the competing plans touches the areas west of Kennedy. Eglinton (west of Kennedy) is getting the LRT line, but that's settled and is independent on the Kennedy - STC corridor.
If you have access to a car and/or are reluctant to take transit (maybe for age-related reason?), would you take the subway, when it is more inaccessible, doesn't take you to where you need to go, and requires convulated bus route transfer that dumps you off in a pedestrian-hostile location?
Which pedestrian-hostile location; STC bus terminal? Riders at Finch / Kipling / Downsview terminals weren't told they suffer in pedestrian-hostile locations.
Or, are the streets pedestrian-hostile? Maybe, but how would the light rail plan change that? That has more to do with the existing built form.
Or, how about the most important question for a Scarborough commuter:
Would this subway extension to Scarborough Town Centre help me bypass the Bloor-Yonge transfer?
Which of the competing plans for Scarborough would help with a transfer to Yonge (either at Bloor or at Eglinton; both are bound to be quite unpleasant)?
The only schemes that come to my mind are a GO-RER / SmartTrack line directly to STC, or an upgraded SRT extended all they way to downtown. While some of such schemes were posted on this forum, the city officials never considered them formally [perhaps such schemes are too far off the beaten path for them].
The official #1 alternative to SSE, aka the light rail plan, would have exactly same problem with the Yonge-Bloor transfer as the SSE plan.