Sure. You can absolutely limit the player's agency in that way. It's an understandable decision to do so, and clearly a lot of people like to go that route.
But then typically we get into these weird arguments about how it's not a limit and their games have as much agency as others and all that. Despite the conscious and willful decision to limit the agency in this way.
If the GM took control of your character and had it make ten really big decisions that drastically changed the setting while you watched... that doesn't feel like agency to me.
Agency is about players.
I get it is in the name but I think the meaning of that term usually refers to agency of the character in the world. When people complain that their agency is being taken away in a railroad, they are usually not complaining that they don't have the ability to say introduce an element of fiction to the world, they are complaining that their choices they make through their character are constrained
I would reject this definition. What you are talking is certainly something that matters a lot, but it isn't what I would call, and what I think not what most people would call, player agency. I think this is more about power levels at the table. Also when you start talking about it as such, it just because easier to speak about. If we are constantly conflating agency of me in the game world, with things like how much GM authority a player has, that makes these conversions confusing (and I think we see that in how they often play out)
I would agree with this, I do think it is an unnecessary tangent on my part to raise that point.
Well, don't think you can really measure agency in a game in "can decide more thing therefore more agency" kinda way. Because certain kind of agency requires some limitations. Otherwise a game with ultimate player agency would be one where the player just produce whatever fiction about their character they wish, unrestrained by established fiction, rules or other participants.
Yeah. This is why I don't like social mechanics that compel my character to react or act in certain way.
I think it usually refers to players. If we talk about it in terms of any non-RPG game, then it's crystal clear. So speaking about it as a quality of the player seems appropriate.
I think when players complain about a railroad, it is exactly about them not being able to introduce an element of the fiction... an element where they decided what they wanted to do instead of having to do what the GM has said they must do.
Well, sure... I can understand your impulse to want everyone to change how they talk about things to match yours, but I don't think that's necessarily a reasonable expectation. Nor do I think that "most" people view it as you do, nor do I think that it would matter even if they did.
But I don't think it actually does most of these well. In fact D&D's rules often don't help at all, or even make some of these harder. To be clear, I'd say the same about actual explicit toolbox systems like GURPS or BRP as well.For me this aspect of D&D is its strength. It has both broad appeal, making it easy to get players for and it can be many different things. I can use it to run a sandbox, dungeon crawls, mysteries, paths, epic adventures, city adventures, etc. it is easy to adjust to a groups preferences (at least I find it so). Another aspect of it is the core components basic set up work. Something about sitting down with a PHB, DMG and MM to flesh out an adventure/dungeon/map/etc just always feels approachable and smooth for me as a GM. I don’t get as much opportunity to play it though these days
Again, I think we just disagree, which is fine. Or perhaps we agree, but you are expanding that point of agreement into territory that feels to me not covered. I don't want to belabor the point. But I think railroad complaints is about players not being able to say things like "Okay we tell the duke to screw and go west instead". It is about feeling like there are rails on the adventures and no real other options, and the player feeling like no matter what their character does, it doesn't matter. But I don't think the complaint is usually made because the player wants something from the system in terms of power, like narrative control.
So in the sense that it is about the players wanting to be able to decide what their characters do in the setting, I would agree. But if we are talking about things going beyond that, I think you are stretching how most people think of agency in an RPG
I don't think railroad complaints about agency are a system complaint. They are a GMIng style complaint
I don't think we are going to resolve this disagreement. But I think I am using a much more standard definition of the term here. And I think it is very reasonable to push back on a definition that seems to come loaded with stylistic preferences. I am not saying those preferences are invalid, but binding them to agency, muddies the water because it confuses a discussion about how the system approaches things like the power of players over fictional elements in the setting, with one that is really supposed to be about being able make meaningful choices in the setting.
I think this is a bit of a misunderstanding/mis characterization. It's easy to address concretely. In Dungeon World the players have certain inputs to play. First of all there's the fairly universal "hey, let's run a game. I have this system, what do you all think?" This is of course system transcending. Then we specific inputs in DW.If that greater ability comes from outside your PC's sphere of knowledge and Influence, it is unwelcome to some. Certainly I feel that way.
I think your use is far more about stylistic preferences than mine. The term as I'm using it is the literal definition when we combine the two words player and agency. Yours limits it because you think of a player exercising agency in a way beyond their character is undesirable.
As for power of players over fictional elements in the setting and being able to make meaningful choices in the setting... I don't think these are different things. I think meaningful choices is one example of the power players have over the fictional elements.
But there are other examples, as well.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.