I skimmed through the previous comments, but I'm not sure I got all the nuances, so I'll go with the initial question. My answer will still reflect a couple of things that have been mentioned already.What do you think? Do you think of world building as largely a GM responsibility? Do you think of the "game" as a whole as a shared responsibility? Do linear games versus sandboxes versus railroads/rollercoasters versus free for alls fit in?
My answer to the second question (shared responsibility) would be a sound yes. Even though the roles might be different (especially in traditional games), a successful game IMO requires active contributions by both players and GM.
The answer to the first question is a bit more tricky. Discovery of a fictional world and experiencing stories is one of the main reasons I play RPGs, and for that discovery to work, the facts about this world cannot be created by myself. Traditionally, these facts would come from a published product or the GM's imagination and that is also the dominant part of how world building happens in the groups I play in.
Yet, there are multiple "buts":
- Even in very traditional games, we have developed consensus that it actually improves the game if people ask leading questions or express theories about a foe that establish new facts in the current scene. Something like "in the walls of this derelict castle, is there a crack large enough to squeeze through and get to the inside", or "this ominous tree at the other side of the river, that is surely a sign of demonic influence". The GM can decide if they want to take this up, and potentially also ask for a skill check, or refute and potentially offer an alternative to achieve the same goal.
- To a lesser (1) also happens for larger things like: "This city must have trade with the Dwarven hold in old times. Are there remnants of an old trade route that we could follow to make sure we don't get lost?"
- And tying in to question 3 (sandbox): it is possible, but not necessary that the GM knows about potential obstacles on the way. Random tables and dice rolls that they then interpreted (potentially assisted by the players in a spirit similar to what I outlined before) on the spot in the context of previously established facts are equally fine.
- Similarly, it is also fine for me, though bordering on falling into another "bucket of fun", if information about aspects of the worlds are established by another player, as long as it is contributed through a lens of their character. Example would be the player of a barbarian relaying facts about the culture of the tribes in the northern tundra, or the player of an elf talking about the habits of their kin.