Some specific responses.
"Also, since we know cooperation exists and is better than non-cooperation, but we also know that disagreements will always crop up, then the above statement can be modified to this: it must be that the DM has the last word on some things, and the player has the last word on other things, when disagreement rears its ugly head."
then down to
|"For the entire history of the hobby, the consensus about who has the final word on what, the line of demarcation, is that the player has the final word on their own PC and the DM has the final word on everything else."
First, not that is not true. Referencing this "hobby" as a whole there are a friggin ton of different approaches to this issue - some offering quite a bit of overlap and crossing back and forth - at the table level and the system level - so the key part is that rigid hard lines of demarcation often are not as rigid as say some gaming theory philosophy-dreamers want to always point things to be. For instance, it may be that the situations allow the decisions to be voted on - where no concrete line of "your or mine" are made other than case-by-case group decisions on policy. other cases, Another vantage point might allow the GM to step in and veto (no that cant happen) but said veto is not used except in extreme cases. A fairly obvious case IRL may be a player acting in relatively bad faith who goes PVP even though it is not normally something done at the table - even if not expressly forbidden.
The thing about choosing to want to prop your position up on rigidly defined lines is that most often in real play these lines are not so rigid or absolute and you may wind up dancing on a theoretical pin that is very much far afield.
And of course, there are numerous examples of very fun games where the rigid absolutism of PC vs everything else was handled not at all as you suggest - games where characters woke up amnesia and had no idea what they were as far as "player stats were", games where screentime type of alterations to the world were firmly in the hands of players and the GMs - etc etc etc. games where NPCs can influence PCs and even change them by "social mechanics". there are RPGs where the actual story/plotlines/challenges are generated by the players much more than the Gm - each resolving pieces as they unfold. cases where the "task roll" for a search is a roll to narrate and create what *is there* as oppose to "find what was pre-determined to be there or not."
And of course, plenty where that gets muddled mixed and matched every day.
In my games, i take the opportunity when a player rolls a 20 on a skill check (proficient) to draw from a list of their background elements and suggestions made by them for inclusion of extra stuff. Some of it was "fleshed out my me" based on what they gave, some of it was created by me to add to what they gave and some of it was created by them and dropped in as is. So a search for a mountain pass might come across a dead body that has ties to one of the players and drives (or provides a new) personal storyline that was not there before. In my game, each player was given a chance to invent a world and race for the game as NPCs and then we worked together to revise after they had enough experience with setting to see whaere they wanted to tweak it.
There is far more in heaven and earth and the rpg hobby, Horatio, than is able to be supported by your narrow, rigid pillar of demarcation that you need to support your arguments.
"So that's why your objection to my fluff is not valid. It would be valid if my fluff choice changed the way lycanthropy worked in his game world for any other creature, but my circumstance is unique."
I get you want to keep piling on things that *may* play a role or *might* play a role so as to keep working until you get the other side in your collaboration to just give up on your wanting to be the only civilized barbarian in your world. the circumatsnaces that allowed you to be such are declared from on high by you to be unique. thats cool... wonderful and fine and all... but for me thats not a collaboration but a dictation. you have taken a rather tired trope and tried to lock it into this "radical concept" of a civilized barbarian (ahem TARZAN ahem) and the equally radical concept of pregnant-when-supernatural trope.
i hope that works for you in your games. I hope you have GMs who ooohhh and ahhh for it.
me? i dont have any problem with civilized barbarian or alternative fluff. i have a problem with unliateral pc declaration of off-limits tho when those are declared.
See, here is the rub... your PC, your bastion of MINE MINE MINE MINE HANDS OFF MINE MINE MINE is, get this, part of the world too. You are not "somewhere else". That means i have to account for you in that "world of the GMs" and just to be clear i am not going to try to take time to list for you everything that might be a problem within the game before you pick up a pencil.
hence that whole -collaboration thing instead of the rigid line in the sand.
That way we get a very extremely large set of things to work with without an amazingly large list of edge cases trying and failing to nail down all the catches and bumps.
"(werewolves are immune to normal weapons; I have a diluted version which explains the damage resistance from Rage, and better Unarmoured AC), "
So, somehow the immune to non-magical weapons somehow morphs into higher Ac vs spells? That chosen and as an unassailable choice by the PLAYER?
Wow... so if a player decided "i once drank gold dragon piss from a silvered boot under a full moon while reciting the oath of office to a town that no longer exists and so i have the ability to backstab as a rogue... the Gm has to accept that because... the player decides its unique enough?"
yes an extreme example but - once one accepts that unique is in the hands of the player...
"I have the right and responsibility to choose my class and background (and, yes, fluff) from those the DM has already said are available."
if you Gm told you that werewolfy sex tricks tropes can give you unarmored defense - then yep - you can choose it as part of your collaboration.
But, beyond that, its more like a collaboration.
An expectation that "all that is allowed will be listed ahead of time" or "all that will be disallowed will be listed ahead of time" - either way - is an unreasonable burden to be placed on either side of a collaboration on a work as broad as these are. Whichever side has that burden is put in the place of de facto forfeiting his side of the collaboration (trusting to the others not just good will and good faith but having sufficient knowledge to avoid clashes) or presenting a massively restricted set of options or presenting a massive list of edge cases.
Not a way i want to work out a game with my players. We come to it with the idea that we all get a good grasp of the basics and general boundaries but that we also expect a lot of possible scrapes and edge cases here and there that we will *work out* and not see as *one side is absolutely right* at that stage of world+PC chargen.
if this extreme works for you - thats fantastic.
