If a JetBlue-Spirit merger flies, it's likely to have a similar result: instantly creating the most complained-about airline in America and delivering substandard service for years to come.

The complaint ratio of Southwest Airlines, which had a meltdown in December that resulted in about 17,000 canceled flights, increased from 1.4 per 100,000 passengers in 2021 to 6.8 in 2022. “Air ...