Yikes. It's unfortunate that so many people insist on taking the same, most direct, familiar route all the time.
For instance, given that bottleneck, I have several preferred routes if I want to get to TTC/PATH from GO. The best route would probably be to go down into the Via departures hall, not arrivals, walk up to the great hall, head outside briefly and take the stairs back down to the TTC, or bypass it entirely and enter the path at RBP or Brookfield if I'm heading north. Or, take the bay east teamway--west is likely a little too busy--and walk up to front, cross over and take the stairs down.
That said, it is pretty ridiculous that they STILL haven't opened the moat or any other alternate passageways in the immediate vicinity of that route, especially after closing the last bit of Bay.