Here are the latest comparisons between the 3 legacies:
Pilots per plane:
American 15.0
Delta 15.1
United 17.0
Forecast hires 2018 (per APC):
American 900
Delta 1200
United 450?
Actual hires 2017:
American 637
Delta 1082
United 428
Hiring historical:
https://fapa.aero/hiringhistory.asp
Mandatory retirement 2018, 2019
American 528, 637
Delta 353, 448
United 398, 411