Pedantic
Legend
We're doing immersion again? That mostly just leads to a lot of subjective statements that could just as easily be read "I had the most memorable time when..." or "I had the most fun playing..."The most immersive games I have ever played are what has been more recently labelled "FKR"!
(Our label for them is "diceless RPG" because those we play use a mixture of drama and karma, not fortune.)
I offered a mechanical understanding of immersion here:
[...] Immersion is resolved at the level of player decision making, and decisions are more or less immersive the less space there is between the analysis of the character being portrayed and the analysis of the player making decisions for them. You can decrease the level of possible immersion a decision offers most quickly by giving the player agency over things (or especially people) outside the character, or by unmooring a decision temporally, thus that it affects past or far future events, instead of immediate action.
A GM cannot achieve immersion in the role of world builder, that is at direct odds with the goal. It is possible to do so while providing agency to a NPC, but probably harder that it is for a player. GM as referee doesn't have a character to relate to, unless we're directly personifying the rules, so immersion cannot be a concern.
It's very nearly the same as my initial post about how to define to a narrative mechanic, but is more specifically concerned with the incentives faced by player and character. There isn't any point to a discussion of immersion unless we settle on what it is and what mechanics encourage or discourage it.