Priority baggage handling is very hit and miss in my experience, too. It is a weak point for sure on AC.

Way back, in the days of Canadian Airlines, I found the same thing. I once had my bag left behind on the ramp in Calgary in the pouring rain due to weight issues on a flight to Lethbridge that was priority tagged (they used Alberts Citylink BAE 32s on that route). That was quite annoying as I could see the thing sitting on the ramp and was powerless to do anything about it.