While I completely agree that AD&D was both a rather complete system (especially for the time, and considering what the systems were addressing at that point in time) and a toolkit (so many options especially in the DMG, but even the PH), I think there was much more than OD&D in there, but a huge amount of production from Gygax and a few others. The amount of material in AD&D is enormous, just take as a simple (imperfect, but still telling) metric:
- AD&D Core (PH + DMG + MM) = 130 + 240 + 114 = 494 pages (A4)
- It's very hard to find the equivalent with OD&D, my version of Men & Magic has 114 pages, but they are extremely small, I doubt that they contain 25% of a AD&D PH page.
- Holmes: 49 pages
- Moldway: 68 pages
- Even adding all the pages of all BECMI books together, I doubt that you get to more than half the core AD&D published in a very short time.
Admittedly, it's not all of fantastic quality, especially the editing, but the amount of material is enormous (just look at spells and monsters list, plus all the races and classes, etc.).