Whoo boy. No. Introduced to D&D as a player in 81 with no rulebook access. Picked up the 1e DMG and PHB immediately after that with NO other experience. Had absolutely no experience with OD&D or B/X prior. And had no trouble reading either publication cover to cover or understanding how to use them.
You greatly underestimate the capabilities of the people, and the complexity of the subject.
Of course, that was with a different US educational system than the one we have now, which is widely regarded as having failed our students, so that might be true NOW. It wasn't in the 80's, cause I assure you, I was far, far, far from alone.
No, that has actually more to do with the fact that the 1e OA book was so overpowered compared to the rest of the 1e oeuvre that it couldn't really be played in conjunction with them. You either had a OA campaign, or you didn't. OA also wasn't a really good product in other ways either. To put things in perspective, Kara Tur (the FR Oriental Expansion in 2e) was a better product and better received. Which is a very telling for OA, because that's not an easy bar to fit under.
Eh-eh. Hand wiggle. I loved the 3-ring binder format - even if I didn't take full advantage of it - but the actual content wasn't noticeably standout.
<snark> You mean the three books I didn't even know existed, despite having been actively playing in FR when they came out? Those books? </snark> Sigh. Sorry. Truly, I have no idea which three books you're even talking about, which strongly argues against their inclusion in a top 50 best-SELLING product list. (Edit: Misremembered - 'twas a popularity poll. Not sales.)
But as for your first point the individual opinions after the OP are almost certainly showing a generational bias, if solely because ENWorld has a fairly significant bias itself.