WRT: The Motley Fool article:

I think the author misses the point that Delta can adjust capacity very easily. (And I believe this is what FlyZ was alluding to.)

Let's take ATL-AUS as an example. Suppose there are 4 MD-88 flights a day. If traffic picks up they can up-gauge the size of the aircraft and/or add another flight. If traffic shrinks they can use smaller aircraft and reduce frequency.

But carriers like SWA or Allegiant or Spirit can't really fine tune their capacity by changing aircraft size. They can only increase/decrease frequency.

I would argue we have more flexibility than those carriers.