To the first point, I think you're absolutely right. Fare integration is not enough. We need the systems to interconnect physically, and we need the GO system to run much more frequently. Luckily, that's already on the books, but for some date very far in the future.
It seems clear that there is demand for an easterly north-south express line, that such a line will take a load off Yonge, and that the beginnings of such a line are already in place. Why is this not a higher priority?
To the second point, you're focusing on the wrong part of the line. Langstaff is not the station which will most benefit. Oriole and Old Cummer are -- as the packed west-to-Finch bus lines attest to. The trip from Old Cummer and Oriole to Union is much faster than riding the bus to Finch, transferring to the subwaym and taking that south.