If tomorrow, DL replaced ASA with Skywest or Compass--all 850+ flights--performance would be even worse considering ASA at least has experience in figuring out ways to work around all the sh## that gets thrown around in ATL. "Tricks of the trade," that is.
I don't know what DL is bi###ing about. They know as well as anyone else who is responsible for any delays in and out of ATL and mostly everywhere else. If the pilots and the FAs show up to the plane on time, which is pretty much all the time, and the plane isn't broken, which happens as often as any other airline, the only other factors are outside of ASAs control and, apart from WX, completely in Delta's control.
As far as customer service, last time I checked, all of the customer service agents in every station are not ASAs. They are handpicked by DL. But realistically what airline in the U.S. has good customer service? If you mean FAs, I think many of our flight attendants are pretty good considering that most of the time we deplane, I hear passengers saying "thank you so much" to the FA or "you were great!"
As far as pilot crews, I see room for improvement in the aspect of customer service. Yes we do have a role. When we are in a money line and it's been 25 minutes and I ask whether or not you want me to make an announcement and the captain says "yeah whatever, if you want"--I think we have some room for improvement. It's not that I want to get on the radio and talk to the pax. It's because it's awful to sit in the back of the CRJ200 for 30+ min on the ground and not know what's going on, especially when you can't see out of the windows properly because they were designed for couches.
Other than that, which is very trivial, I don't see the issue here. Skywest would fail miserably here as well as anyone else who took over the burden ASA has.