This is in my view absurd. It implies that a player is
breaking the rules if they make any response to a GM's proposed fiction other than - what - just getting up and walking away? (Or is that breaking the rules too?)
It's a game of collective make-believe. Page 2 of the 5e Basic PDF sets it out like this:
Together, the DM and the players create an exciting story of bold adventurers who confront deadly perils. Sometimes an adventurer might come to a grisly end, torn apart by ferocious monsters or done in by a nefarious villain. Even so, the other adventurers can search for powerful magic to revive their fallen comrade, or the player might choose to create a new character to carry on. The group might fail to complete an adventure successfully, but if everyone had a good time and created a memorable story, they all win.
But you're saying it's
against the rules for a player to point out that something the GM is putting forward is neither exciting nor apt to be memorable nor leading to a good time.
As I said, that proposition I regard as absurd.
I agree it is absurd for anyone to think the players lack the power to challenge a DM on their proposed fiction. It is the DMs job then to refute the challenge and explain why the fiction is as presented. Discussion and debate can then lead to a happy conclusion for all--if possible. However, there will be times when compromise is not possible, at which point those players (including the DM) simply don't want the same sort of memorable, exciting, good time and can part ways amicably enough IME.
FWIW, I think any sort of this "challenging" should be done outside of game time if at all possible. Game playing time is too precious IME to waste with such things and players (hopefully?) trust their DM enough to just "go with the flow" until such a time that the discussion can be made.
However, I will restate the DM is the final authority when it comes to the narrative fiction of the game and the game world implications. The ultimate power of veto a player has is to leave the game.
Can you think of examples where player knowledge would really matter?
Certainly. The precise eye-beam abilities of a beholder, for example, should be a mixture of actual truth and rumor / mistakes as well. Beholders (thankfully!) are very rare creatures in D&D games IME. What incredible powers a beholder actually possesses should be rare knowledge requiring consulting a sage IMO.
The more common a creature, the more widespread and accurate the knowledge in the game world should be IMO.
For example, the contenious kobold is uncommon in AD&D, not common like the orc or ogre. As such, general information and opinion (evil, wicked, vile little things kobolds, are... kill ya as soon as look at ya) should be typically known, but as an uncommon creature there is by no means
any guarantee a PC will have ever met a kobold until the encounter one during an adventure.
For example, does everyone at the table need to pretend they are surprised that a Troll requires fire to kill it?
No, but realizing as an uncommon monster there will also be fokelore and misinformation about it as well.
That would feel off to me.
Plus, in a setting where people encounter Trolls, fire would definitely be part of the folklore.
"Aye, sure ya are fire is the bane of a troll! But it only works during the day I tell ya!--At night, fire won't stop them monsters from coming back from death to kill ya!"
And often depending on the rarity of the monster, that fokelore should be misleading or even outright wrong.
"It'aint fire, ya idiot, 'tis water that the trolls have a bane for! Like witches, water will melt a troll away! Why do you think they hide under them bridges? To stop people crossing the water!"
Again, if the DM really wants to surprise the players, create a different kind of Troll. (Norwegian folklore is full of extremely different kinds of troll, if looking for inspiration.)
Well, here's the issue with this: if the players
know before hand that the DM will throw all sorts of different monster variations, great; but if not, players will often complain "but that isn't what it says in the MM!!!"