But that's why I say it's more of an open ended RPG, because the role of your character is something you set yourself rather than something that the narrative strictly sets for you. There are tons of non RPGs that have an established character. I mean really, CODs, Portal, you name it, has an established character, and those clearly aren't considered RPGs. Whether you like it or not, Dark Souls is by large considered an RPG.
You know, I think the gameplay loop is very important in defining an RPG, because obviously from the examples being given, the narrative/character style varies greatly within the RPG genre, and just because a game has an established character doesn't mean a game is an RPG. I never called NMS a straight up RPG, but saying it resembles nothing of an RPG is a bit ridiculous. It has the standard RPG gameplay loop of grinding resources, allocating them into a skill tree, using your upgraded character be able to fare against stronger dangers, repeat. RPGs typically have that gameplay loop, making it RPG like in that sense. You play a "role" in RPGs (along with many other kind of games), and you can play a "role" in NMS. The only difference there is you're choosing which role you want to play rather than having a strict narrative tell you what you're doing, which again, just makes it open ended rather than something that's defined by cutscenes or something, but it's still playing a role nonetheless.