This very interesting video came out from the YouTube channel Questing Beast:
I think that many of the points made here are pretty accurate: D&D was originally written to house a large group, where a player might have multiple characters, and a single referee was seen as running a world, not a storyline. This is certainly what we see playing out in the early days of Alarums & Excursions, when players would bring their characters into other referees' dungeons – and sometimes clashes of expectations resulted.
This is, of course, why time is so important as a resource in the game. The video is quite right in identifying and laying stress on this part of game management, and it makes sense of many of the fiddly time-related rules in AD&D that, in a standard heroic campaign, seem simply like a matter of tedious bookkeeping (and possibly to allow things like weather or dungeon repopulation to factor in).
And it's accurate to say that this style was somewhat submerged. I think that this was a result of the shift from play in large, open groups of high school or college students (as was often the case in places like Wisconsin, Minnesota, and California), to small, closed groups of middle school students, in the explosive growth that D&D went through in the early 1980s. When these players, who learned RPGs from one of the Basic Set boxes, transitioned to AD&D, they lost the idea that the game was designed for large, open tables, and began to play out quests that would look more like modern D&D. And the modules changed to accomodate this – it's not a coincidence that Ravenloft and the Dragonlance modules happened around this point in time.
I think it's somewhat narrow in its view, though. In the early 2000s, the West Marches reinvented this style of play, recognizing that even though 3e D&D had a fundamentally un-Gygaxian attitude to its rules, the notion of a large open-table campaign was still part of the D&D rules. Even 5th edition, with its time-intensive downtime rules, still has some elements that fit into this style of play. Today, West Marches style games run in 5e are such a popular format that it has its own category in areas where people look for games.
A lot of the old school ethos applies directly to this kind of game. It's fundamentally about place and exploration – one of the "three pillars" of D&D play, according to 5e. It de-emphasizes the role of the player characters as world-shaking heroes, but gives them the opportunity to become significant political players by building strongholds. And it places a priority on strategic engagement from the players.
In terms of rules, this is where the D&D Rules Cyclopedia has probably the strongest support. BECMI D&D developed the idea of domain management into a fully fleshed-out system, which a lot of clones haven't bothered with. One will notice this, for instance, in a clone like Old School Essentials: there are tight procedures for dungeon and wilderness exploration, but as far as domain management goes, it simply features a few paragraphs about clearing the land and some prices for castle structures.
To be clear, this wasn't part of B/X and as such their non-inclusion isn't a fault of OSE – but the domain rules in the Rules Cyclopedia are only a few pages long and fill out the processes that have otherwise been left vague throughout D&D's history. This has been one of the consequences of the OSR generally following the lead of B/X D&D and not BECMI/RC D&D in its mechanisms of play. Of course, there are reasons for this: many players have the most fun running and playing D&D in the adventure parts of the game, and B/X is in many ways the cleanest approach. But it seems like there's possibility, in the large-scale game, to really embrace and extend things beyond the individual session.
I think that there's a lot of fertile ground to develop procedures and methods of play that are specifically geared toward large play groups. An old school equivalent of Izirion's Enchiridion of the West Marches (itself a useful resource for any referee) would be, I think, one part of reviving and supporting this style of play more broadly.