I'm sure retirement numbers used to be on APC, but I can't get the search here to look further back than a year, but I did find a post over at flightinfo.com that had United, CAL, DL/NWA, and AA numbers on it.

https://forums.flightinfo.com/showth...ry+retirements

Based on this data, which was posted back in 2010, I can only look at United vs DL, because the US Air and SWA numbers aren't posted there.

Also, the USAir hiring numbers aren't posted on that other database posted earlier.

So, if you just look at DL since 2013 until 2017 (since 2018 isn't over yet)

The numbers come out to:

Net gain in pilots
UAL DAL
2013 -20 -139
2014 -48 +677
2015 +485 +680
2016 +84 +876
2017 +353 +696

That makes the total for the past 5 years where United has gained a net of +353 pilots and DL has gained a net of +2790 pilots.

And yes, there were furloughs that returned at United that would obviously taint the United data and reduce hiring, but at the time,2013, all but a few CAL furloughs were back on property, and probably at least a third (guestimate) of United furloughs were already back on property, possibly more. So even if you give United an extra 1000 pilots to account for furlough returns, you still have DL doubling the "growth" of United over the past 5 years.