Actually, the situation is that those tracks are also used by freight trains, and GO can only run trains in one direction. Yes more people are going toward Union but the lines don't just serve Mississauga. GO is currently building a third rail to accommodate all day, two direction service. If there was no demand for this service, they would not be investing in it... Plain and simple.
The article you posted shows exactly what everyone here is trying to say... more people commute to Mississauga than commute out of Mississauga. That means it is not just a bedroom community anymore.
Your own source also shows that only 29% of Mississauga residents work in Toronto, while 55% work within Mississauga. Again, how does this prove your point?
As for your second source... I see way more dots south of the 401. Going with what you see though, that area is Mississauga. You can't just move borders to prove a point. That isn't how the world works, regardless of how you see it. The reason why there is little to no residential there is because of the high aircraft noise. That area is Malton, and it has its own history. It has since become part of Mississauga and while it may be separated by Canada's largest airport, it still functions as part of the city.
PS. Your PS. is exactly what people have been telling you...