Hm. I'll have to look at this later, depending on how much I can stand. My guess is that I won't be able to stand very much.
The last time I seriously looked at GNS, my takeaway was that "Simulation" was an equivocation. The theory defined unintuitively compared to the plain English meaning of the word (it's basically a branch of narrative), and then later on discussions repeatedly use the plain English meaning. I don't know if it's an intentional choice or what.
However, GNS seems to try to stick a bunch of things into a bag and call it simulation, some elements of which come from the narrative aspects. Then it tries to elevate actual realism and make it equally foundational because simulation. And then justifies it by saying you need a consistent narrative for N and S and that's two-thirds of the game... in spite of the categorization not necessarily being equal divisions. It's a confusion of ideas, but maybe it's my confusion.
I do think well-designed TTRPGs are built to express ludonarrative verisimilitude if you want a $50 term for it. "The game mechanics reinforce the truthiness of the fiction, and the fiction enhances the truthiness of the game mechanics." The introduction of an implicit or explicit feedback loop between the narrative and the mechanics creates the overall game. I think that's basically all that separates a TTRPG from a legacy boardgame or wargame league. (But... also I don't dislike legacy boardgames or wargame leagues!)