Narrativism can be broadly defined, and so is role-playing. Lucky for me, I evolved my ideas of what D&D should be in near isolation, and took at face value that DM tells a story of what is going on, and the players tell him what their characters do in that story, and the rules are used to make realistic outcomes.
From the beginning I realized that the D&D rules as presented, were not realistic, too abstract, too based on luck and too linear, so I broke away from it. Over years I realized the moral implications that D&D suggested, an old cop, when I explained D&D to him, laughed and said, "your D&D adventure is basically an armed robbery - break down the door, kill the owner, take his property". Later still, I realized that miniatures is not the most accurate way to portray combat or make the characters visualize or experience it. I became a fan of phenomenology. And so, I became a fan of my very own historically accurate and tactically realistic, thoroughly fantasy sand-box.
Railroad adventures give narrativism a bad name. Most sand-boxes and hex crawls fizzle, because they lack the conflict and urgency of a story. Some DM's call Sign-posting, the practice of telling the players exactly where the DM wants the players to adventure in his sandbox. I reject sign-posting, and boss monsters, and power-players, and make my rules the bane of any power player who tries to figure out the optimal approach, by basing it on what is known in the real world based on research, and nothing is more complex or overwhelming than the real world.
And so, almost all the players I had have been uncomfortable about getting into character and role-playing, and I don't have a problem about players talking in the third person: "Zorg does this... Zorg does that... Zorg". One guy was stammering and was clearly uncomfortable with dying people screaming, crying and begging for mercy, or having to role-play his character comforting crying children who just lost their parents. In his case, the limits of his emotional depth interfered with him interacting with the game world. He stayed. Another quit. My best player never role-played, and when my players got into character and actually role-played, the players' agency (initiative and ability to get things done in the game world), went through the roof. So, I am not forcing the players to role-play, and can get along without any, but I sure am glad, when it happens.
I consider myself a narrativist DM, in that D&D is a storytelling game, mind, not a choose your own adventure, not a scenic train taking people from scene to scene, however, the sandbox will lose all meaning if the campaign doesn't have the beginning, middle and the end game; if the conflict and the march of events does not touch the players, and if it doesn't have some value/reward system beyond the level advancement and the loot. In my campaign, the players are egg-shells floating in the ocean near the shore, and the campaign is a breaking tidal wave that will throw the players on the shore and smash them against it. Where and how the players will end up, is up to the players.