That a given person ignores something does not indicate that said thing is not implied.
And those game rules imply elements of setting. If it tells us part of how the world works, it implies setting.
First, that means that any system with magic has an implied setting. How magic works is absolutely part of a setting.
Second, D&D spells, annd Spellcasting, are very specific. Tasha’s Hideous Laughter implies the existence (past or present) or an arcanist named Tasha, and further implies that spells can be created or invented, and thus sometimes get named after someone.
And since that name can't be used in a non-OGL-5e-alike, that bit of world doesn't actually exist--and it shows that the name of the spell isn't actually important, since plenty of OGL-5e-alike games are using a non-Tasha's hideous laughter
spell without any problem.
It's also something that can be very easily ignored or adapted even in a regular 5e game. Just ignore the lore behind the name and decide Tasha was someone else. There are probably a lot more people who know the spell than who know of the actual character's history and lore, after all, and there's nothing about the spell that says that it must
be authored by a very specific Tasha, student of Baba Yaga and who went by Iggwilv.
The mechanics of banishment, certain warlock patron abilities, even the text of Divine Sense and Detect Evil and Good, imply that beings come from other planes of existence, and that their nature is tied to the planes and to ideas of Good and Evil in some way.
Right, but this is a very light implication--and one that is very
easily ignored. If you want all your fey to be happy-fun bundles of chaotic goodness, you can. If you want all the fey in your world to be the grimmest fey imaginable, the type that will smash the world if it would make a pretty noise, you can. If you want there to be no
fey in your world, you can, and all you'd have to do is disallow or rename one archetype and maybe a couple of invocations.
And when you get down to it, even how most of the classes work is really up in the air. It's why there's so many discussions as to whether or not patrons can yank the spells of warlocks who aren't serving them properly. When it comes down to it, the only real lore is saying "warlocks get their powers from powerful beings who aren't gods." That doesn't say what or who those powerful beings are or how they grant the magic, just that powerful beings exist. One could even interpret this to mean that you could have a warlock whose patron is a much-higher level mortal fighter. Hey, why not? Basic D&D had Immortals, after all. Maybe any PC who hits 36th level can start handing out warlock powers now.
The warlock class would
be lore-dependent if, instead of the book saying "your patron is an Archfey," it said "your patron is one of the following: Neifion, Hyrsam, Baba Yaga, Lurue, Titania, Oberon, or Verenestra." Because that seriously limits
So that's literally all I'm talking about here. How much of a setting is going to be implied in these rules? Is it going to be a game where anyone can make a world that looks like anything they want, or is it going to require the presence of specific, named people, places, things, or events?