@Faolyn , I'm not the folks you're interacting with, but I'm going to throw a few (lol?) words at the conversation you're having. I'm also going to use the term "say" here (meaning "player's say" or "system's say" rather than "GM's say") in the stead of Railroad. Here are some examples that are either significant input into/over the trajectory of play via "say" or significant reduction of the same via lack of "say."
* Do the players have
say over what this game is about? Does play chase what the players are interested, which they've signaled either directly via words or indirectly via system components (like relationships and dramatic needs) within character build? This one transcends serious. Its pretty profound in its impact. If this is not true, that is a an
extremely substantial reduction in player (or system) say.
An example of this would be this week's two Stonetop sessions where the Spring Bursts Forth move ushered in a Threat and an Opportunity for the Stonetoppers, the thematic content of which was authored either directly (corrupted, massive, Xenomorph-ey insects are haunting the forest on the doorstep of Stonetop) or indirectly via player's words or things like a relationship on their PC sheet (their parents advancing age and needing relief in the way of more goatherders in Stonetop). And then you have the play engaging with their instincts of Curiosity, Honor, Balance, Charity.
* Can the players consult the accumulated wisdom of their played character via (a) putting something provisional out there about the shared imagined space that could end up being interesting and useful to their situation, (b) staking the prospect of their memories/education (etc) being erroneous and the actual truth of things complicating their lives (via GM getting to say what is actually true), and (c) putting that to the test via action resolution mechanics (of one form or another). Do players have the
say to attempt to stipulate consequential things their characters know and have that impact the gamestate/trajectory of play? If this is not true, that is a
reduction in player (or system) say.
An example of this would be the Seeker (sort of an Antiquarian/Loremaster/Warlock character) pouring through her tomes to try to assist with useful information an expeditionary force of Stonetoppers who are going out into the wilds of The Flats, sending their midwife and a section of soldiers, to deliver a child of a group of Hillfolk goatherders who have recently lost their midwife. When this move turned badly, I turned their move back on them and took the hopefully interesting and helpful information and made it hazardous to the point that they had to devote more assets to the field to lure a group of Hillfolk raiders away to ensure that a terrible fate doesn't befall the primary expeditionary force. Well...both the move for the main expeditionary force went poorly as did the move for the daredevil cobbler who was convinced (by that same Seeker) to run interference against the group of Hillfolk raiders.
Things went very south as a knock-on effect of this move. Them's the breaks. But that is how "say" goes. Significant trajectory of play is put into effect, good or bad. This same Seeker had multiple such knowledge moves go right for them in their expedition/adventure to save the deadfall-gathering children who were captured by these aberrant swarms of insects and that led to positive gamestate/trajectory of play and the player fleshing out the world through their character's inventorying of their substantial knowledge.
* If Inventory/Gear decisions are supposed to be compelling and important for the trajectory of play, does the situation framing and the resolution mechanics allow the players to have such a
say over game-layer-engaging, situation-impactful Inventory/Gear decisions? If not, that is a
reduction in player (or system) say.
An example of this would be the Lightbearer character in the Stonetop game (who is an Itinerant Mystic with Gandalf qualities whereby they can show up with important information or have an esoteric bit of kit). The Lightbearer had a rare collection of mashed material components to load out in a smoker which allowed them to potentially Keep Them At Bay (the aberrant wasp swarms), spending the precious fuel of this apparatus while forming a sort of pike hedge as they dealt with the swarms via a concerted volley of spears by the Marshal's Crew, the Ranger peppering arrows, and the Seeker throwing burning pinecones.
* Are the framed situations/obstacles put before the players engaging, impactful, trajectory-of-play-dictating such that
players have substantial say over the game's fiction and game's state when engaging with and resolving them? Are their decisions meaty, consequential, thematically compelling, tactically/strategically engaging (decisions to chart this course vs that course or to deal with this potential suite of complication vs that potential suite of complications or to choose this complication over that complication when things go awry...or to skillfully choose and put into effect this particularly impactful line of play vs these other impacful lines of play)? If there is a reduction in any of these things above, or an arbitrariness, or a signposting/signaling of consequential decision-points that are actually just feigned/falsely signaled?
The reality is GM's can be better or worse at building out a vital decision-space of game layer intensity. GM's can be better or worse at engaging (and that could be at the conceptual or "build" level or the communication level) the players with a meaningfully and consequentially different decision-tree to navigate and resolve. GM's can be better or worse at "employing the rules and letting things fall where they may" once player : situation : system collide. Well, as GMs are worse at any of these things above (rather than better), that yields a
reduction in player (or system) say.
So,
reduction in say (player or system or both) isn't any one thing. And certain types of reduction in say are more impactful than others (and some of that will be game-contextual). But a thousand raindrops make a puddle, as the saying goes, and as that drip, drip, drip accrues, the reduction in say can drown out the player's consequential impact into the content of and trajectory of play...and there is absolutely a point of muted player input where you're effectively a bystander.
EDIT - I need to include this because it is an example that isn't GM-related. The same is true if a player doesn't know the full rules of a game or how all the rules come together. Player's can absolutely
reduce their own say (and they might be totally fine with that...but that doesn't mean that their gamestate-&-fiction-impacting footprint isn't reduced) in this way.