Even that I'd disagree with. But I was responding more to the first part of the statement, "RER exists not to serve people living by the subway commuting throughout Toronto", which, even taking into account the second part, is a pretty strong and inaccurate statement.
Of the
12 new stations being built (13 if you count Park Lawn), only 4 are outside Toronto. Yes, that story is almost two years old now but the point is the same. GO has historically been suburb-focused but one of the main reasons for its expansion is to vastly increase its relevance to Toronto itself.