Interesting take on this incident and the Northwest distracted crew here, It's a sensible argument but I'm not sure I really agree - I think it's too narrow. Clearly the actual potential consequences of the NW incident on the day were not as serious as the DL landing at Atlanta, but I wonder if that's really the point. The question is how come that NW situation could have arisen, and when you've worked out how come, what other consequences could have arisen from those factors in different circumstances. Ditto the DL incident of course.
So DL may perhaps be more important than NW, but until you've worked back to the root causes you can't tell.