Do you think everyone at the Legacy airlines sits on reserve??
Typically reserve coverage is only 20% of each category, that means 80% of the pilots are line holders. And with a wide variety of fleets, pilots can pick and choose their relative seniority, to either be junior at a higher pay rate, or get senior and off reserve. This month our 777 reserve lines are paying 82 hours, and lots of very senior guys bid to be on reserve, they know they won't fly much, if at all, and still get 82 hours.
Our trip rig is 5:15 day minimum, so to get to 75 hours they'd have to fly about 14 days, which is why International type trips go senior to our domestic, they fly more hours per day, so you are gone less days to get the same hours...
and when you go to the Hotel, it's a nicer hotel in a nicer city and for 24 hours, vs. 9-10 hours at the typical Airport Holiday Inn. Back in the Good Old Days, the most senior trip was on the L1011 out of ATL, doing a San Juan turn, it was about 8 hours block, you flew it 10 days a month for 80 hours pay and slept in your own bed every night. It went very senior!
SWA has always been more efficient on a per day flying basis, because they only fly one airplane type, so everyone is qualified on every airplane, so there's no need to deadhead in an A320 Crew on a MD88 to cover a mechanical, etc. So you average more flying per day, vs. a Legacy hub and spoke type operation with many different fleets, all sitting around ATL or DEN or ORD waiting for their type of aircraft to arrive.
That's a very ineficient use of the pilot's time. We call them "Productivity Breaks", when we get stuck in the hub for 3 hours waiting for our airplane to arrive. That crap gets old fast, which is why most guys go to Int. as soon as they can hold it.
I said a long time ago, if Delta wanted to match SW in terms of efficient, they should just buy 500 737's for domestic flying and another 200 767ER's or 787's for International flying, but they'd also be able to get by with 2,000 fewer pilots to cover the same block hours.
Life is about choices, an all 737 airline doesn't give you much choice, but hey, who wants to get paid to fly to Rome and layover anyway?