Well, Southwest was a successful well-run regional carrier that grew as large as the big mega-airlines, while trying to keep running the business the same way.

There are still 20 smaller regional airlines in the U.S. and hundreds around the world. The vast majority of those fly just one or two types of planes.

> And yet many airlines fly a very high amount of planes of many types, of multiple brands

That's simply untrue. Most airlines use 2, 3 types of planes at most. I'm not referring to the niche 5 percent of plane types but the overwhelming majority.