So here's a data point that I found interesting. In 2 years of flying the YYZ-YVR-NRT route, I've had an occasional delay ex-NRT due to congestion on the taxiways, but I've never had ALL FOUR flights on a single trip delayed.

AC 153 was delayed an hour due to late inbound international aircraft

AC 3 was delayed 2 hours due to late inbound international aircraft

AC 4 was delayed twice for a total of an hour. First was late inbound AC 3. Then we sat on the taxi way (while NRT airport ground crew drove up and down inspecting the runway. Kind of cool to watch but still)

AC 102 was delayed for idiocy: 40-50 pax were stuck in line at the security checkpoint. Apparently CATSA decided not to have enough screening lanes open

I felt really bad for all those people at the YVR gate for AC 3 who knew they would miss their onward Asia connections. Same with some on AC 4 who would miss their domestic.