Both me and Pemerton have addressed this point. I think we made the point somewhat differently but essentially described it more as inhabiting the character than as performing. There can be performative aspects to it, but I don't worry so much about them. This is particularly the case on the player end. As far as I am concerned what matters is the first person, not that the player portray a character. They could be playing themselves in the first person and I would be fine with it. Obviously the GM has to run multiple characters who exist in the world, so they need to account for things like personality and knowledge the character has. But I don't expect a performance in the sense of using voices, gestures, etc.
Again, I think so much of this thread is really about playstyle. And you see that when we talk about playstyel differences. I think talking about the specific example is much more productive than the general rules and general terms (because the terms are quite broad, and obviously there are places where I may agree performance could matter). It is just the way things like performance, presentations, etc have been used are done so to paint a picture of RPGs that doesn't match how Pemerton or I see the game. When we talk about specifics, it becomes easy to hash over those differences. When we talk in generalities, it becomes more like maneuvering a chess piece in the conversation to force people to accept specifics before they arise. I am really not trying to be difficult here. But I've just been in enough of these kinds of discussions to get that. And I think it is important to push people to talk about what they are really talking about. And what we are really talking about isn't categorization or modeling of the RPG experience, we are talking about how we want the game to be run and how we want games to be made (and you see that because it repeatedly comes up and people repeatedly argue over it).