I think you guys are looking into it too much. It's just a promo to hype up a match on a b-tier PPV. They've been doing these "shoots" for a while, they know it's an easy way to get smarks who claim they don't care about Cena or Reigns invested in the match.
Oh it's for sure been the standard Cena vs X promo that they've been doing since the Edge/Cena feud, where X calls Cena out on all his shit, and then Cena completely eviscerates their gimmicks or angles to the point where it doesn't matter if Cena gets squashed after, he already won the feud. But usually, it's built for the other guy to get major digs in on Cena, and the other guy is a smark fave with more cred than Cena. In this case, Cena is the one with the credibility to the audience, he was the one who got all the major digs in, on top of doing his character assassination stuff. Shit made no sense.
Never mind that they're doing another "everything else is fake, but this is REAL" build up to a fake fight. If you can't do a good promo that doesn't kill the nature of the rest of the show, then don't do the promo. The example I've been using for years now is if Walter White turned to the camera and said he was Bryan Cranston, then shit on the writers/directors because for a few minutes, then went right back into the normal show. Or if Walter and Jesse were in the middle of a scene and he started calling him "Aaron" and talking about how much he sucked.
Everyone knows its fake, but when the show is on, they don't want to be reminded of it. It's a TV show like anything else and it would be ABSURD for something like that promo to happen on anything else, yet this is the standard Cena promo and somehow it works every time for a certain portion of the crowd. There's no benefit to publicly excoriating the guy you've built the company around in a "real" promo for the benefit of a guy who used to be the face of the company but now is doing as much outside work as he can so he can get out. In the case of someone like AJ/Punk/KO doing a promo like this, I would say it would get that portion of the crowd even more on their side, but in the case of Roman, it felt like they were just throwing him to the wolves for no reason.