> Southwest should be more resilient in some ways in that all of their flights are done with the same type of plane, so they can always swap in a different plane for the task

That's not that unusual for their size airline. But, some of their planes have more seats than others, so on fully booked routes, swapping in a smaller capacity plane is still a problem. Certainly, a smaller problem than if they swapped in a plane the current crew couldn't fly.

I don't know where other airlines keep contingency planes, but I'd imagine they might keep them at their larger hubs, which would give you a decent chance of having a contingency plane at the right location; with Southwest's model, I think any contingency planes are going to have to first deadhead to the route, adding more confusion and delay. :/

At least they fixed this one quickly; once the backlog got too big last time, it was very difficult to fix.