These are some great thoughts on the divide, but I want to clarify my point some.
I think there are two tensions going on for the majority of D&D's lifespan: For argument's sake, we'll call them rules and adventures but that a bit of an oversimplification: Rules refer to the actual rules of the game, while adventures how actual play was thought to go (both in terms of purchased modules and design principles). Lets grossly simplify them thusly:
OS rules: random generation, high lethality, DM fiat, zero to hero progression
OS adventures: exploration-focused, player challenging, combat as war
NS rules: concept focused generation, recoverable losses, more concrete systems, PCs start out heroic
NS adventures: story-focused, character challenging, combat as sport
When OS rules meet OS adventures, you get the proverbial Keep on the Borderlands/Tomb of Horrors style play. When NS rules meets NS adventures: you get Paizo adventure paths. When NS rules meets OS adventures, you get Dungeon Crawl Classics (the modules, not the RPG) and when OS rules meets NS adventures, you get the bulk of 2nd edition.
Which is why I say NS begins far earlier than 3e; AD&D started out OSR/OSA, but after Hickman began to move towards OSR/NSA, with the rules slowly dragging their feet towards NSR inch by inch. Neither happened overnight, and it isn't until 3e that we really get NSR/NSA styles aligned. (and even then, Goodman proudly produced OSA for NSR, it was their tagline).