That's always a concern, and will never be resolved perfectly. No matter what route is chosen, some residents will feel they got short-changed.
In case of the OL west extension, possibly it would be best not to swing the route south from Queen to the Exhibition, but rather send it north-west to meet the Bloor subway and then serve the area between Bloor and the Spadina subway route.
However, once it is settled that OL runs to the Exhibiton (far south), getting it back to the north of Bloor is a nontrivial task. Need to make a tricky transition from westbound at-surface to northbound tunneled, and then cover some distance in the tunnel.
Therefore, I feel that a new subway line from the north-west is better off going straight into downtown (under Dundas), rather than veering south all the way to Exhibition to link with the OL.
That's a thought. I have always seen the logical place for OL to go as up Jane or Dufferin, but perhaps you're not wrong. That being said, where does OL go from Exhibition?
I see a couple of options. The first is a line down Queensway. This is fairly straight, but there's perhaps less room to put another rail corridor south of High Park. A logical extension would be to build Waterfront West LRT, then connect a median LRT down Queensway to that (or the 507. Your choice).
DRL West was always going to go up towards B-D. However, there's no logical route north of Exhibition for it to follow.
We could permanently terminate it at Exhibition but that leaves extra capacity through downtown. One thought could be to turn it up Roncesvalles, and have the KING car terminate at the carhouse. It would go towards the Junction and perhaps terminate at Eglinton (after connecting to the 512). This would mean that to get from B-D to the 504, you'd need an extra transfer. Don't know if that's worth it, and I don't even want to see the pitchforks aimed at me for that proposal.
That being said, fare integration between GO and TTC would make life easier for Humber Bay Shores residents sooner rather than later. We should be aiming to service denser areas with higher capacity transit, and any OL extension westwards would take decades - I don't see it coming before 2040.