I also find it fascinating digging into the transition and the extent to which AD&D was a new game (as Gary insisted at the time) or was "just" an expansion and codification or new edition of OD&D.
Gary decades later said it was all one game, and the editing of AD&D, and all the stuff they left out which they had told us in OD&D makes that seem much more true.
And it's a shame that he gave such a contrary pitch in the 70s and 80s. Because there's a ton of useful stuff in OD&D which legions of us never saw until many years later, believing the hype that AD&D was a new and complete and superior game.
Well, I think that this is one example of where the text ... matters.
If you were only aware of the LLBs from OD&D, sure, AD&D might seem like a completely new system. But the vast majority of the rules in AD&D are just the following:
LBBs + Supplements (aka, OD&D) + The Strategic Review + Dragon Magazine.
There's very little that is "new" to AD&D. Sure, some of the rules are tweaked, but even the core classes are simply codifications of classes that already existed! The only real major change was turning the ... ugh, I hate talking about this ... Bard from a regular class to some kind of bizarre proto-prestige class in the appendix. Sure, the DMG greatly expounded on all sorts of issues, but, again, very little was new- that's why I've written before about the interoperability of the TSR systems. If you were playing OD&D plus supplements plus keeping up with the official TSR magazine, nothing was very surprising in AD&D.
As for the dice and rolling abilities, I think that the section speaks for itself; the Methods were presented as alternatives to the baseline of rolling 3d6 in order. Again, you have to remember that there was a default assumption that was behind how people were playing back then. That's not to say that other people hadn't explored alternate methods before that; it's sort of like the discussion around critical hits! Despite Gygax being famously against critical hits (and therefore, no critical hits in TSR-era 'official' D&D until the optional rule in 2e), there were people experimenting with critical hits prior to that- even in OD&D.
I do think that the presentation of alternative methods (which culminated in Unearthed Arcana ... ugh) did show the shift in thinking on the part of Gygax. From viewing PCs as normal people who went on adventures to being, themselves, exceptional to start with. Which is probably a separate conversation. Or, as I often say, if you want to find a quote that disagrees with Gygax, just read some more Gygax.