I'll start by admitting that I have not read every exchange in this thread.D&D, and 5e, also has a traditional play loop. The three-step process is described in the 5e PHB on page 5, under "How To Play":
"The play of the DUNGEONS & DRAGONS game unfolds according to this basic pattern:
1. The DM describes the environment. ...
2. The players describe what they want to do. ...
3. The DM narrates the results of the adventurers' actions. Describing the results often leads to another decision point, which brings the flow of the game right back to step 1."
So far, so obvious, right? Notice that this play loop, as described, tends to lend itself to a certain division of authority. The players have the authority over their characters to decide what to do, and the DM has the authority to narrate the results and describe the environment. This ties into another aspect of D&D ....
If Rule 0 is about the DM's authority over the world, then Rule 1 in D&D is about the Players' authority over their characters.
If you only play D&D, this might seem banal to the point of uselessness so far. The idea that a player has full control over their PC is ingrained, at this point, that there are many people who play 5e who argue that even spell effects that negate player authority over the PC's decision making (such as charm, or any controlling spells) should not be used on PCs.
To get back to the OP, what's at stake here is the 5e play loop as described by the book. Specifically what happens between step 2 ("player describes") and step 3 ("DM narrates"), and how much agency does step 2 give to the players (and I think agency is a useful word here). That is, does the players having agency rely on the 300 pages of rules that follow this described play loop from the 5e introduction, or is it already contained within the basic play loop?
Two extreme examples: a player says that their character would like a new mountain range to appear, without reference to any specific rules, and the dm says, "no, that's not possible." Is that indicative of a denial of player agency? Or, a player says their character would like to go talk to the blacksmith, and the dm says, "rocks fall, you die" for seemingly no reason. Is that outside the purview of the dm, who is in control of the world?
My opinion is that the 5e play loop accords plenty of the agency to the players--they have control over their characters--but also depends on everyone being reasonable and acting in good faith. The DM, in step 1, should have communicated a particular type of world, usually in dnd one that resembles the real world for most ordinary actions but with some exceptions for the fantastical. The rules are there to provide a further framework for what's reasonable for a player to attempt in step 2, and a guide for adjudication for a dm in step 3. So there is nothing in the play loop formally to prevent the dm from declaring "rocks fall, you die," but informally there is an expectation of reasonableness and a framework for adjudication that imply that dm ought to not be so capricious with step 3.
I would further say that the play expectations and social contract are more important than the rules in 5e. If you have a good, trusting dynamic with your group, you can forget or get plenty of rules wrong and still have a good game. But if you don't have a group with trust, then the rules will just give you another thing to argue about (in fact, I would speculative that you could keep the basic play loop and get rid of all the rules and things would still work out, but that's for another thread...). This is why 5e communicates to the dm that the goal of being a dm is to ensure the players have fun. This is mostly a positive direction for the game, as it mitigates against adversarial dming. It's less good in that it can turn the dm into a kind of entertainer, ignoring rules not to say "rocks fall you die" but instead "you are successful in standing underneath the falling rocks, but you don't die, because you are important to the story."