I don't think that it really makes sense to talk about a "sim aspect" to fiction writing. Simulation is an attitude towards, or an approach towards, playing RPGs, that is concerned with how the various participants orient themselves towards the shared fiction (both as an input into, and an output of, their collective game-playing activity).
There is no shared fiction of that sort in fiction writing. REH is unequivocally the author; and you and I and other posters in this thread are unequivocally the audience/readers.
Sure, but there can still be an attempt at inserting a level of plausibility, just like I mentioned with the professional wrestling example elsewhere.
Even if the booker is in charge of all the storylines (and is essentially the author,) there can still be an effort made to simulate varying levels of an athletic contest. While they all fall under the umbrella of "pro wrestling," Japanese 'strong style,' lucha libre, 80s NWA, and 80s WWF all have very different approaches and varying levels to what's real and what isn't.
Similarly, REH has an approach to writing the visceral nature of combat (sites, smells, sounds) and tactical engagement that is very different than authors who may place less importance on that sort of thing. I don't think it's a stretch to say there are reasons for why his writing eventually came to be defined as a separate genre.
Sure, playing an rpg and writing a book are two different activities, but I posit that they are both approaches to creating fiction and writing a story. As a game is essentially a group effort at creating fiction (albeit one in which there are asymmetrical roles when it comes to GM & Players,) having a shared sense of what type of story -what style of fiction- you want to create and experience matters. Mechanics are a piece of it, but the "how" and "why" you choose to approach it matters just as much.
The group having some common ground for what's real and what isn't... where extra detail matters and where it doesn't... are we working lucha or strong style? ...if this was a movie, are we thinking directed by Tarentino or Michael Bay?
Maybe the terminology doesn't exactly line up 1-to-1, but those sliding scales and knobs can still be adjusted. Creating a sim aesthetic requires a certain set of choices to the approach. That's just as true for writing a battle that feels 'real' as trying it is for trying to play through a game that feels the same, even if (and I would say especially if) we're including elements that are fantastical by their very nature.
