it's pretty strongly implied there that we have polytheistic worlds right out of the gate.
Even Moldvay Basic states:
Clerics are humans who have dedicated themselves to the service of a god or goddess
And Acolytes are listed in the monster section as having any alignment.
Again, I'm completely baffled where this notion of monotheism comes from and how 5e is somehow different than pretty much anything that came before.
Being dedicated to the service of a god or goddess permits polytheism. But it doesn't imply it. In the first ever Moldvay Basic game I GMed, one of the PCs was a cleric, and while I don't remember much about the details of that game, I don't think we ever thought of the religious/cosmological situation of the game as being polytheistic. And as I posted upthread, polytheistic clerics give rise to the inevitable question -
why is the cultist of [the Rat God; the god of forest ponds; etc] wearing mail and wielding a mace just like a mediaeval holy warrior?
Yes, there are evil as well as good clerics (and potentially neutral ones too, though not originally in AD&D) - but the implication in early D&D can easily be drawn that these cultists draw their power from dark "gods" who are really demons etc.
While I believe invoking Tolkien in these discussions is pretty much analogous to Godwinning a thread, I'd point out that in the Hobbit and the LotR, religion plays pretty much zero part in the fiction. There are no priests, no churches, and, AFAIK, zero mention of any religion whatsoever. Granted the Similarian changes this and adds to it, but, if your knowledge of Middle Earth comes from the first two works, it wouldn't be hard to think that Middle Earth is pretty much godless. It's not monotheistic.
There is no organised religion portrayed in the Hobbit or LotR. But it is not godless.
Someone sent the Istari to Middle Earth, and then sent Gandalf back. And Gandalf confronts the Balrog with the words "I am a servant of the Secret Fire, wielder of the flame of Anor". These are religious allusions, although one needs to go to the Silmarillion to get any detailed sense of what they are allusions to.
the DM is the arbiter of the setting, and the non-player beings in it. If the divine gets involved in the game, it will be the DM making the decisions as to what happens.
This
may be true of some games. It may even by
typical of all games. But it is not universal.
In the games I run, the GM doesn't make all the decisions about the actions of the divinities. A good chunk of that is determined by the players of PCs who serve various gods.
plenty of people worship a monothoistic deity, but if they're deeply religious it doesn't matter whether D&D replaces their deity with one different fictional deity or multiple fictional deities
As long as it's not their deity it's idolatry to them
I don't think Yaarel agrees with this at all, judging from this post:
Do I want a monotheistic campaign setting? The short answer is, yes.
<snip>
In a monotheistic game setting, the Divine normally intervenes only subtly and indirectly, because, the Divine desires humans to make the world a better place by means of human effort. The risk to humans is real. The good that humans do is real. Normally God is hidden. God is most ‘visible’ when other humans are doing good things. In other words, if the DM wants to supply the team with help via some NPCs or items whose opportune timing is ‘miraculous’, that can be fine and fun. But in terms of actual game rules, monotheism is part of the background flavor without any need for mechanical rules.
As I read it, Yaarel thinks that the way to incorporate monotheism into the game isn't by making up an (imaginary, therefore false) divinity, but by allowing the essence of the divine to be expressed in in-game events in just the same way as (a monotheist of a certain type believes) the divine essence expresses itself in real-world events.
I don't want to push the theory of divinity any further, for board rule reasons. But assuming I've properly understood Yaarel's approach, I can see at least two implications for game play arising out of it:
(1) Maybe there are no clerics - or perhaps clerics get reconfigured as a species of wizard; but any character can, via his/her actions, reveal the divinity at work in the world. So there is no special category of persons ("clerics") who are uniquely able to do this.
(2) The GM can't have the unique authority to determine the ingame significance of particular events occurring; and nor can players be obliged to see the roll of the dice as modelling nothing about the gameworld but the random chaos of a cold, indifferent cosmos. This latter approach is a good fit for a Conan-esque game, in which the world is cold and indifferent and humans must make their own fortune through self-assertion (of the sort that Conan excels at). But in a game of the sort Yaarel describes, it has to be open to a player to understand an ingame event which - mechanically - may be the result of a random die roll as expressing, in the fiction, the workings of divine providence.
The games I GM tend to exemplify (2) - I see this as a necessary condition for the RPGing of a truly
faithful character to be viable - but not (1), and so they wouldn't satisfy Yaarel's desire for a monotheistic game. (Assuming I've understood that desire correctly.)