Spirit is a real player in the ULCC/LCC space. They have a big boy contract and their hiring teams absolutely hate the idea that pilots might be simply touching base there on the way to a legacy. They did it to themselves when they ****ed off so many ex-military pilots who gave spirit a try but were disgusted by the idiocy displayed by spirit management during the contract negotiations, but the sentiment is real. Any hint that spirit is just a touch and go and the application will likely get sorted to the circular file. Mil pilots spent their mil career with an incompetent leadership chain that has permitted work conditions and compensation to continuously degrade, and they're not willing to work for a company that is running the same playbook. Pilots with a purely civilian background who have a similar attitude might find it hard to get hired at spirit especially now.

For a pilot with 18 or less years remaining (ie. many retired mil), the career compensation (to age 65) at spirit and SWA are nearly identical, but the flying at spirit will be 2-3 leg days with a 5 year upgrade, vs. 4-5 leg days and a 10 year upgrade. An older pilot with 10-20 years remaining may actually get paid more for less work at Spirit than SWA. That may change with 2020 but it's shaping up to be a battle.