"One side can just say 'no, screw you, we do it my way" is not acceptable. Period. Neither side gets license for that.
I do not know how to explain it any simpler or differently.
If the DM can, at any time, unilaterally reject anything and everything the player says, regardless of reason or sense, then they are the only one who actually has any agency or control. The players are simply present for the experience. If the DM happens to feel like granting something, it has literally nothing to do with their responsibility to listen to requests. It has, only and exclusively, to do with them deciding what to do with their unilateral ability to declare what is and isn't. The player request is a grace note, nothing more.
If the DM is required to listen to any reasonable request, and to do what they can in context to fulfill those requests, then (by definition) there must occasionally be times where the DM would rather not do a thing (or do a different thing), but they are obliged to do so because the player has a reasonable request that can be fulfilled in context. Likewise, if the player is obliged to keep their requests reasonable and to adjust within reasonable limits to that game's context, then there must (by definition) occasionally be times where the player would rather not do a thing (or do a different thing), but they are obliged to do so because the request isn't reasonable or cannot be fulfilled in context.
Neither side gets a get-out-of-discussion-free card. Neither side gets to dictate terms to the other. Both must recognize reasonable limits and both must accept that they might be obliged to do something other than what they would prefer. Rendering default judgment solely because someone is DM (or player, or whatever) is declaring that the other side must, always, put up or shut up, unless the dictating person is so gracious as to not raise a stink about it.
Being dependent exclusively on someone else's graciousness to get anything at all that you want is not a discussion, nor does it mean requests matter. It means you are acting purely on that person's positive feelings, and the instant those feelings are gone, you get nothing.
