Are you sure agency is the right term to use here? It at least seem used for very different purpose than common in RPG discourse, where typically power and agency is used somewhat interchangably. You might want to clarify how you intend the word to be understood. I do not think the Calvin ball example is sufficiently illuminating, so you might want to look for some thing else, like "meaningful play"
It might be better to pick a different one. There are clearly two different conceptions of agency...and both sides think their method leads to more agency.
Perhaps we can frame them as agency as player and agency as character.
When I as a player say "my character examines these runes" or "my character picks the lock", I am asserting agency as a character. My character interacts with the world and to the extent that the world is fixed my character's actions have specific effects that can improve the game state.
When I say "I hope the runes are this", roll and that becomes reality, I'm asserting agency as a player. Or perhaps an author? I'm authoring new fiction to generate the outcome my character hoped for.
My point is that these two types of agency are opposed. For agency as character to be meaningful, the actions must be interacting with an objective game state. If I read the runes, get a 10+, and they turn out to be beneficial, I didn't exercise meaningful agency as character because I didn't take a specific action which improved the game state. Instead the roll led to meta result of good and the player was permitted to author some new fiction.
From the character's perspective...the author is still not
me. It is someone else. And the fact that someone else can roll dice and see what happens with my life, and this takes precedence over the actions I choose to take, means I have very little agency indeed.