I agree with others that it's a difficult job and that there will always be a "bad player" here and there. All of this is based on impressionistic thinking, but FFIW:
- ATL is by far the largest hub, therefore with the most GA. There is a higher probability of running into a not-so-good GA there, as they also must move between different gates, sometimes with no warning (i.e. frustration and time pressures).
- YMMV: it is always about the last impression one had with such things, meaning the most recent input is always the strongest for psychological reasons. This works in the other sense too, e.g. I had a terrific experience in LAX in the past two month, although the ground staff there seems to have a (IMO) not so good reputation.
To me, it always helps to ask, how I would feel if I could imagine myself in that situation? There are a few very bad employees at any large company, but for the most part, it is simply someone having a bad day, often for reasons that aren't clear to the outsider.