The more I think about it, the more I'm convinced that the concept of a "living world" by itself is a net neutral correlation to "immersion."
All of the "offscreen" gyrations/permutations/extrapolations of what NPC/faction does what, where, and why, is not really important for my ability as a player to be "immersed" moment to moment.
During the times when I was most "immersed", these were the common components:
- I had a strongly-realized character. The character was easy to visualize within the fictional space, with strong, well-defined motivations.
- The immediate scene being played out directly connected to the character's motivations.
- As a player, I was open and willing to let the scene play out organically. I wasn't going to just "do this thing because that's what my character would do," I was actually trying to interpret the in-fiction results of the game loop into the frame of the scene. If something changed in the fiction that would have mattered to my character, I wanted that change to be accurately reflected. To be clear, this was only partially carried out in "actor" stance. There was significant bouncing between actor and author stances, interpreting the character within and the scene without.
As a player, nothing about the GM's conception of the "offscreen" world made any difference in the moment.
Conversely, some of the most anti-immersive things I've experienced were related to my inability to pursue my character's dramatic need. I'm specifically thinking of the Savage Worlds Shaintar game my friend ran three years ago. There were many, many moments where'd I'd try to get "in character," start to picture how my character would react in situations, how she would view/approach certain NPCs, etc., but would constantly get blocked when I realized that
this character was being denied what she would have wanted.
The only way a "living world" construct makes any difference to me as a player being "immersed" is if it gives the GM the ability to create scenes with 1) stakes appropriate to my character, and 2) is willing to actually "play to find out what happens."
For example,
@Bedrockgames has cited multiple times a quote from a module that talks about how "the goblins don't just stand still," or whatever; i.e., the dungeon/town/city/country evolves as time goes on. But the GM's background workings/methods/processes in regards to making those extrapolations ultimately have zero effect on how and when the next
scene of play has the ability to "immerse" me as a player.
I think what I'm getting at is that "living world" sandbox play has a number of merits in and of itself, but there's nothing about the GM functions/machinations involved in generating a "living world" that would have any real impact on my "immersion."