Except every possible avenue you might pursue with those choices was designed by the actual creator.
That's not true at all. My character's motives are entirely mine. His decision-making process is mine.
I don't get direct control over anything that appears on screen, but that content's metadata (for lack of a better term) is created by me.
Your collaboration is an illusion, because you don't own any of the responsibility of the creator's job. You aren't held accountable.
Yes I am. I'm responsible for my own enjoyment. No one else could be, because no one else knows what I like.
If I ask a bartender to make me a drink with part this and part that, and then drink it in some creative way, I don't share ownership of the drink with them. I'm still the consumer. I can control the speed at which I drink and the size of my sips, even whether/how much I warm the glass with my hand and possibly ruin my own drinking experience, but I still didn't make the drink.
But you were a co-creator of the experience of drinking it. You helped create the story of the drink.
Story requires conflict, usually some kind of obstacle in the way to the protagonist's happiness. To have that, something must be assumed about the protagonist's interest.
That would only be true if the source of the conflict was created aolely by the designers, but that's not necessarily true.
A player could create his or her own objective for the character, and the conflict would be that character's struggle to achieve that objective within the rules of the setting. The authored narrative created by the developers then, would serve as flavour-text for the setting of the actual story, whichbis the emergent narrative created through the player's choices.
In Mass Effect, does Shepard trust Udina? Did Shepard want to become a Spectre? What is Shepard's opinion regarding any one thing in the story? Do those opinions ever influence her decisions?
If you have any control over the answers to any of those questions, then you're creating story-relevant content.
The protagonist can't just walk into a room and hang themselves, and they can't just sit in a field and smell flowers the whole game.
They could, but it would be a stupid thing to bother designing in a game. Total freedom isn't a plausible consideration, there will always be a boundary.
Freedom and control are not the same thing. Stop equating them.