I've seen similarly chaotic boarding at several of the YYZ T1 INTL gates, so in my limited experience, I don't know that any one of them is worse than the others.

I would also point out that it doesn't take much for any particular boarding process to become chaotic, even at places where that isn't normally an issue. For instance, IAH is usually pretty decent, but the other day they let a woman hold up the Z1/2 line for several minutes while she waited for her husband, who was off doing something else. Right behind her was a man pushing his wife in a wheelchair who had either not shown up in time for pre-boarding or the agent had not properly managed the process.

Meanwhile, Z3 boarding was started, from the other podium, leaving a number of Z1/2s fuming in the other line and trying to jockey our way over to cut off the Z3s so that they didn't get on and hog all the bin space.

Plenty of space in that area and usually not a bad place to board, but totally bungled by the GAs on the day and it became about as chaotic as it can be for a 76-seat CR9 (which is a different kind of chaos than boarding a 77W, for sure).