Agree with the latter, though not as much with the former. Even in B2, the iconic example of the wild frontier module, the setup is that Chaos is threatening and encroaching on a static border, rather than as in the American West where it was "civilization" which was expanding.
Largely agree.
Heinlein would have strongly disagreed with your translation. He definitely didn't believe that might makes right, nor was that what he was positing in the book. (we've had long discussions about the book elsewhere).
In the sense that you're using the term "narrative", xp for treasure or for killing monsters are equally narrativist. They're conceits of the game to incentivize characters to engage in a specific style of play. Advancement by the chunkier "number of sessions played" count is just a less granular version of the same thing. The behavior being rewarded is basically "adventuring" in both cases.
In real life experience in fighting does improve certain fighting skills (though it often comes at the cost of PTSD and other long term wounds, tangible or intangible), but training is a much bigger part of it ("the more sweat left on the training field, the less blood lost on the battlefield" I believe was one of Col. Hackworth's mottos). And of course no amount of fighting or loot collecting will make you better at academic skills or picking locks.
If you want "learning through doing", you'd want an advancement system more like BRP. When you successfully use a skill you get a check mark next to it, then at the end of a session/rest period/downtime you get to make a test on each such skill to see if it advances.