Not necessarily "GM as adversary" - in narrativist play, for example, the GM should be trying to facilitate the players' ability to make the thematic statements they wish to make.
That's one reason why I talked about "narrative control", to make it fairly explicit what I'm referring to. I'm not talking about a competition for fun, I'm talking about who gets to control the events in the gameworld. Letting the players do more of that, and the GM less, may well be win-win in terms of playing pleasure, but it is still a transfer of narrative control from GM to players.