Kurotowa
Legend
My experience as a player is somewhere in between. I'll come up with the seed of a character idea and then focus on learning about the parts of the setting that are relevant to the character. Learning about everything is too big for me to keep in my head. But if I want to make, say, an orcish war veteran trying to make a new life, I'll look up info about major orcish settlements and recent wars.Let me rephrase. Players very rarely will care as much about a setting as the DM does. At least, that's been my experience. And my experience has also been that the players couldn't give a rat's petoot about setting when creating characters. They come with fully formed characters more often than not and then expect the DM to somehow fit that character into the setting.
Though to be fair, I've totally seen the people you describe who come up with the completely independent character. Or who come to the DM asking for instruction on how to fit their PC into the setting because they're not the sorts who RTFM themselves. But in general, what I see from the player side is people who zoom in on what relates to their PC and nothing else.