By way of the predicate context, the former referent of the term "D&D".
It seems to me that your statement is purely subjective.
At least in the games that I've played in, gamist narrative elements have often been used, even in previous editions of D&D.
A classic example is the cavalry that rides over the hill just in the nick of time. Sure, they might have been teleported there via magic, but it could just as easily be the DM creating an exciting scene (and they've been riding for days to get there in time).
CAGI just puts this power (in a limited sense) within the player's realm of possibility (once per encounter).
It's like an example that another poster in another thread used (sorry, my memory is terrible and I can't seem to locate the post atm). It's an ability called Master of Disguise (from a game called Spirit of the Century) that allows a character to disappear from a scene and later reappear in the place of an NPC (turns out that the NPC was the character in disguise all along). It's very gamist/narrativist, but also very cool, IMO.
As I said, this is nothing new to D&D. Bluff, Diplomacy, and Intimidate were able to alter NPC behavior even in 3.x (it's been a while, but I don't think those proficiencies existed in 2nd ed so there's no real basis for comparison AFAIK). A Diplomacy specialist at high levels could convert almost any NPC into a fanatical follower with a few (non-magical) words.
CAGI isn't necessarily the best designed ability out there (similar in that sense, perhaps, to high level Diplomacy in 3.x), but it also isn't necessarily magic either. It's Conan tricking the enemy into closing with him, for example. Conan wasn't exactly a rocket-scientist, but every now and again he managed to "get one over" on people much smarter than he was. If ever a situation arises where I say
there's absolutely no way that enemy would do that, I'd inform the player before he used his power and that's that. That's partly the reason the DM exists ("No, I don't care what that supplement says, you're animal companion cannot have his own mount".).
CAGI certainly
could have a supernatural explanation, but I honestly think anyone who can't admit that it
could have a mundane, gamist, narrativist explanation is wearing blinders. As for which is a better explanation, I certainly admit that it's open to debate.