You've created a chicken/egg situation by citing the DM's authority as described by the rules. If the DM gets their authority from the rules, then I don't think we can accept that the rules are not the source of authority...
Finally, and perhaps most relevantly, we're not only talking about D&D here. You've quoted the DMG. I could quote other games where there is no equivalent "rule zero" type of text. This is simply not true of all RPGs. I don't think it's true of D&D, but with other games there's not even a doubt.
You seem to place primacy on the rules as written in the book. So I pointed out that the rules as written in the book give the referee authority over the rules, including interpretation and changing thereof. Many other games have similar explicitly stated text. Some don't, sure. Most traditional games and even some non-traditional games have similar text. It's mostly in the indie scene where this norm is broken. So while technically true that not every game has this setup, it's basically irrelevant as the vast majority of games as written and games that are actually played do.
The referee's authority derives from the social contract. Everyone agrees that this person will be in charge of the game. They trust the referee to run the game, provide interesting experiences, etc. Some players insist that trust goes only so far as following the rules to the letter, reducing the referee to some kind of wetware to run the software of the rules. Others are a bit more...open minded about things.
The point of having a person run the game instead of a computer is that freedom of choice. The ability to go off the map. To zig when the module thinks you can only zag. To create and run unique adventures molded to the PCs at the table instead of a generic party. To be creative and make rulings that suit the table. So why lessen that flexibility? Why would you? Just run a solo game at that point or play a video game.
I don't think that the intention is for the DM to simply start ignoring rules and doing anything he feels like.
That's what you assume they will do. Literally no one's said that's what they will do or even want to do. I certainly haven't.
You keep saying things like this as if without the rules as written being followed perfectly, only, and precisely it's inevitable anarchy and chaos. I get that exaggerated rhetoric is just a thing on the internet, but come on. Which is why I quoted chapter and verse earlier. You really seem to be into the RAW as authority above everything else. I'm pointing out that's simply not true.
The point of contention seems to be ultimate authority (as in final say). At the end of the conversation it comes down to the referee and players hashing things out or no longer playing together. But at no point can the players demand and expect the referee to do something a particular way. Nor can the referee demand same. But, as the referee, with all the power and responsibility that goes with it, they can and often do step up to that line. Quite often, the players ask them to. Each and every single time the players do something that's not precisely covered by the rules. They trust the referee to make the call. If the players cannot convince the referee to do it how they want, the players have one choice: stay or go. There's no appeal to authority to be made. That's my point. At the end of the conversation, the referee makes the call. The players can stay or walk. But there's no appeals.
You
do trust the referee to improvise and make up rules to cover the things you want to do, but, paradoxically, you also
don't trust the referee to improvise and make up rules to cover the things you want to do. Seriously. Pick one. Either it's referee as wetware-automaton entirely beholden to the rules, or it's referee as thinking person able to make a call.
No, such authority is given with the expectation of being exercised responsibly.
How is responsibility defined here? Can you recognize that there are different types of responsibility and that what one thinks is being responsible another would think is irresponsible? Once you acknowledge that, this very quickly goes back to trusting each other.
How is such responsible use to be determined? By the participants as a collective, with the text as their guide.
Rules as guidelines, yes. Not written in stone.
If the DM overturns a rule, and a player questions it, I think we can all agree that the DM should have a justification for it.
Absolutely. Now, what happens if/when the players do not accept that justification?
They go back to having one choice: stay or walk.
The bit from the DMG you've cited is not an invitation to just ditch all the rules and do things however you want. Otherwise the DMG would be one page long and all that it would say would be the bit you've quoted.
Again, you instantly jump to anarchy and chaos. No one's said that but you. The fact is the referee can change and interpret the rules. Even without the book making that explicit.
You've flat out stated you trust no players, so I don't know why all of a sudden trust is so important to you. According to what you've said, you trust no one you game with.
Trust is always important. Without trust we can't do anything. Assume people won't break your trust, and when they do, don't trust them after. I've refereed more than played in the nearly 40 years I've been engaged with the hobby. Referees need a whole lot more trust than players do. Players need to be trusted to honestly create a character and honestly engage with the game. The referee has to be trusted with...literally everything else that goes into an RPG. Something that you'd expect your referee to do, like fudging a number on a monster statblock is something you'd bounce a player for doing, i.e. giving themselves extra hit points, spells, spell slots, attacks, levels, gold, etc. The roles are not the same. The expectations are not the same. Pretending they are is not...wise.
Exactly. So why is the imperfect designer who's never met you in your life more trustworthy to make a rule than the referee sitting across from you who's played with you for years? The person at your table knows you infinitely better than some rando on the far side of the country. The rule some designer wrote down is not sacrosanct. The ruling your referee made is not immediately suspicious.
Like, I have people who I'd trust my life with...but I would not let them pick the movie for movie night because their taste in movies sucks. One has nothing to do with the other.
Note how "would not let" in that sentence is you stating you don't trust them. So this person you trust with your life, you don't trust with your entertainment. That's pointing out there are different categories of trust. I'm not talking about trusting someone with your life. I'm talking about trusting the person you already trust with your entertainment...to keep being trustworthy with your entertainment. You already trust the referee with your entertainment, otherwise you wouldn't be sitting at their table. But you, for some reason, don't trust them with your entertainment...despite sitting at their table...explicitly giving them trust with your entertainment. Either you can trust the person with your entertainment or you can't. Pick one.
The kind of "I needs all teh power" GMs that you're describing...
You're mistaking your assumptions about what I'm saying for what I'm actually saying. This is more of the "anarchy and chaos" assumptions you're making rather than what I'm actually saying.
"I don't mind relinquishing my authority to the dice and/or the players" that I'd prefer to game with.
You're wrongly assuming it's perfectly one extreme or the other. There's a vast, vast excluded middle you're leaping right over.