The difference in flexibility between Spirit and F9 is simple

At Spirit you can drop as much flying as the system will allow and never hear a word from a manager Chief pilot or the training department unless you're going to dequal.

At F9, if you don't maintain at least 60 hours per month 6 months a year, and 70 hours per month 6 months per year, expect to hear from your Chief pilot.

The work-life balance at Spirit is far superior.