Disagree
I disagree about the PIC multi/piston vs. single PIC Turbine.
For SWA requirements, they accept all forms of PIC fixed wing turbine. This is a quote directly from their website.... "Additionally, a minimum of 1000 hours in Turbine aircraft as the **Pilot in command, as defined by FAR PART I is required." ....... they go on to say "Southwest considers only Pilot time in fixed wing aircraft."
When all is said and done, you'll have plenty of multi time, but the PIC Turbine is what you'll have to fight for. I'm sure it would be hard to get hired from SWA with just 1000 hrs. of Caravan time. But lets say you racked up some good Caravan time early on in your career (approx. 700 - 800 hrs.). Now you have flown 300 - 400 hrs. at a regional as Captain in a multi turboprop or jet, well you can apply.
But I will agree that multi time is more important in the beginning when you are trying to get that initial flying job. But long term, I would say PIC Turbine - whether it be single or multi.