I'd go with they have their number considering they have a 3-1-0 (WTL) 7 goals scored and 2 goals against +5 goal difference.
It's a bit of both, I'd say. As we've discussed in the match thread Atlanta has always struggled with teams that play a high press AND can do it well. Team Energy Drink does it as well as anyone in MLS because that's their norm, they have great athletes for the job, and their coaches have done well in getting the plan right. So while other teams may replicate the approach (DCU, Abu Dhabi NY...) the results may be less convincing. At stake is the ability to stifle Atlanta's build up from the back. Parkhurst, Pirez, and company are solid MLS defenders as their records show, but as a unit they're not primed for 90 minutes of quick short passes and fighting to retain possession. This is precisely why Nagbe was brought in, to support the transition game. But this is still MLS level play. Pirez can be impetuous, Parky and Larentowicz can only spend so much energy over a match, Guzan is mediocre in his distribution... It's a great MLS side but still imperfect. Teams that can exploit this will tend to succeed. This belies another side of the debate that's missing, which is that RB:NY are a really good team. They're equally poised to set the MLS record for points in a regular season, they're also very experienced and arguably a deeper team. Them beating Atlanta isn't really the story, I'd say, but rather it's how did they trip up along the way that they're still in 2nd place? The fact that they are 2nd implies they're also imperfect, so it's no given they'll hoist the cup. And seeing as the teams have only played 4 times I'm not ready to call that "having Atlanta's number." If it continues through the playoffs then, yeah, that might be a factor because we all know how mind games work. So nothing new was revealed Sunday, IMO.