The whole 'transit-to-the-airport' thing really can become the great white whale of transit planning. As far as overall transit problems facing the GTA, transit to and from the airport is really pretty low on the list in terms of importance. That doesn't mean never invest in transit to Pearson, but 90% of the proposals here are completely overkill for the number of people who will ever ride them. Even the Crosstown extension to YYZ was overkill. Yet here we're talking about HSR, the Finch LRT and god knows what else.
Also, everything in the GTA is a 'hub' now. Apparently there are 51 "mobility hubs" in the GTA. Just calling something a hub doesn't mean there is enough passenger demand to warrant big capital projects.
If any airport needs improvements in transit connections, it's probably YTZ. Considering it's right downtown it's insane how many passengers rely on cabs to get there. And unlike Pearson, the area around YTZ isn't an industrial expanse, so any investment would kill more than one bird.