@Ovinomancer
Your contribution needing to go through a review process doesn't mean that you didn't exercise agency in creating that contribution. Without you there wouldn't even be a thing for the final arbiter to approve.
You've swapped the goalposts, here. I'm talking about doing Thing A. You're talking about proposing Thing A to someone else with the authority to allow to deny. You've dressed this up in "review process" but it's still a shift in what we're talking about. You can propose whatever you like, and, sure, that's some kind of agency in the sense that no one can stop you (presumably). But that agency to propose Thing A doesn't translate into doing Thing A.
We're talking about doing Thing A. As I've already allowed, you have some kind of social agency, in real life, to play act your character however you want. This isn't required by the game, though, so doesn't translate into agency
in the game. The ability to do a thing that isn't necessary to the game can't be said to be part of the game. It's also present in all games, in equal measure, so it's a wash in considerations of agency. The agency in the game is the ability to do things in the game, that are required by the game. These are character actions, and here, looking at the fact that the GM can negate those actions unilaterally, usually by reference to secret fiction, is a removal of agency from the player. This is usually ameliorated by the conventions that the secret fiction is fixed and/or fair and discoverable through actions that will not be negated. This equates to solving a puzzle, and you have some agency here, but it's by those conventions which constrain when the GM can unilaterally negate actions into places where your skill as a player hasn't measured up to the challenge.
So, yeah, there's agency in games where the core mechanic is GM decides. I would not play 5e if this were not true. Agency is present in these conventions that restrain the GM's authority, and are usually unspoken, social contracts that revolve around an also unspoken concept of "fair play." These conventions get breached all the time, though, but rarely enough that they hold in place, or in ways that a particular group has become accustomed to and so incorporated into the unspoken concept of fair play. You see this a lot in the 5e forums, where differences in the understanding of this unspoken concept of fair play between groups clash in discussions on use of Force and fudging. You see it here, where you're bringing along your unspoken social concepts that your table plays by and using those instead of the bare rules to judge the presence of agency. Fundamentally, though, I cannot exercise agency over a thing if someone else must grant permission for it to happen. The confusion I see from you on this is that exact unspoken contract, where you know that a GM is actually constrained by the social conventions of your table (and most tables) so as to not fully have this authority in all cases. This isn't a feature of the rules, or your ability to play-act, but of the social nature of how we do things as people. And, recognizing that the game has moved that there, and what exactly that unspoken agreement entails, can improve your game because you know can go to the right place to tweak things that may be bothering you. I see this misunderstanding all the time in the forums as well, where well-meaning GMs are trying to introduce house-rules to constrain behavior that's enabled by the social contracts in place and so end up frustrated when the game mechanic fixes don't address the problem.
I've put this last bit into practice, by having open discussions of how I will GM in any given game, what I will be held to and what goals I'm trying to seek. I expect players to do the same. This has made, so far, every single game I've played doing this more engaging and free, as players know exactly how I will interact with their play. And, if I don't, they can call me on it.
