I agree 100%. I am not sure how the GM has any sense of exploration at the table in a sandbox though. Discovery and exploration are definitely destroyed by the ability to just make things up. So in essence, I see a need to heavily divide GM-player authority in an effort to allow the player a sense of exploration at the expense of GM exploration.
Please explain how a GM can keep a sense of exploration in a sandbox game.
Maybe you just don't get it - you don't get that sense of wonder, of discovery, from seeing the milieu develop in play. I know I do.
I 'make things up' but I don't know how the players will react or how it will develop in the future. I use a lot of random rolls, I don't know what the random tables will tell me. I didn't know there was a basilsik in that jungle until the dice told me so.
Also, using the published Wilderlands of High Fantasy, it's hugely detailed, I don't and can't know everything there is in the City State or the Wilderlands. So eg in my City State game when the PCs go left instead of right down an alley I'm discovering what's down there more or less alongside them, and riffing off what's described in the official book.