Sure - "to at least some degree". In the case of immersionism, that degree is that the only parts of the world that will turn out to be played in will be those the PCs choose to explore. Generally speaking, player characters in an immersionist game are to some degree exceptional. RuneQuest character arcs take them to becoming rune lords/priests. In Traveller you can start with your own spaceship! In L5R you may be a samurai.
It's not only the exceptionality of the characters, it's things that happen to and around them. Like, goblins don't terrorize the village because of socio-economic reasons, they do it, so the PCs have something cool to do. One way or another, interesting things need to be happening, so the play can commence.
And on the other side of the screen: the
players are often forced to make their characters behave in ways that would be weird for actual people living in this living breathing world. They
have to accept a stranger into their party (or continue adventuring waay after they've already accomplished their goals, or whatever) because otherwise Vasya ain't playing the game.
Let's imagine the immersionist world sans player characters. That does not at all satisfy the itch! It's the opportunity for the characters to explore the world and find out what happens there, that is the draw.
The way I see it,
not having designated PCs, but rather grabbing characters from the world and discarding them as needed would accomplish the exploration of a secondary world better than being stuck in a single PoV for extended periods of time.
First, it limits what cool interesting things players can actually get to experience. As an example, the beliefs and rituals of the Cult of Ancestor Moths in Elder Scrolls are pretty neat, but pretty much impossible to "access" in a game because the cult is very secretive. To explore them is to devote the whole game to it (and then probably end it, as you'll inevitably run out of fuel pretty quickly).
Second, there's only a portion of a world that immerses one in this world. It's kinda hard to put into words, but bear with me here. I really,
really like Elder Scrolls. If Lady Nerevar didn't claim Kirkbride, I'd tie him down in my basement. Immersing myself in the world of Elder Scrolls is something I do genuinely enjoy. Debating the nature and origin of Talos; listening to sermon delivered in the temple of ALMSIVI; crawling through filth in the canals of Foreign Quarters, all that is awesome!
But the process of playing a "traditional" RPG will inevitably include a whole bunch of stuff that has nothing to do with Elder Scrolls. Killing goblins in Cyrodiil ain't any different from doing the same in Phandervel, after all. If anything, experiences that are not unique to Elder Scrolls in any way shape or form will probably constitute a way larger portion of the play process.
Isolating these highs of Elder Scrolls-iness, culling the shackles of a single character to give a damn about and focusing on the world and its lore sounds, to me, like a straight-up better way to immerse myself.
And on the other side, player characters sans world? That's scarcely reflective of most RPGing: players seem to delight in having some sort of world to play within.
Well, it's not like the world
doesn't exist. It's just the world is subservient to the goals of the people at the table. Like Silent Hill, built and rebuilt to specifically torture the PCs, rather than be a thing in of itself.
In the same vein, I'm not suggesting to remove characters and never ever introduce them under any circumstances. No. What I'm suggesting is rather than making them the centre of attention, put them into background.
Rather than having players to control exceptional heroes in a world adjudicated by the GM, have one take on a role of, say, Arcane University professor delivering a lecture on the history of Psijic Order, and players to be her students.
This purpose of rules - to fabricate a mechanism that successfully controls and simulates the desired play - falls outside of viewing play as narrative that "by its very nature places specific people front and centre rather than the world itself." As it turns out, the nature of an RPG can include modelling the world itself. Almost all do, to a greater or lesser degree.
What I mean is, the characters will be at the centre, whether it's a high-octane action film or a simulation of a world with all its mundanity, as everything is perceived through them.