Alright, continuing on:
Is it really? Then why was 3e so allegedly impenetrable for that? You seem to be rather vacillating about whether 5e is special and different or, as I've argued, familiar.
Ehhh. I dunno about that. Certainly it should be something you can explain to children, but an 8-year-old is going to be typically in 3rd grade, which is about when children are first being exposed to concepts like multiplication, division, decimals, and the fundamentals of area and perimeter (that is, basic measurement geometry, as opposed to merely shape geometry.) While I have worked with such students in the past and recognize that they are much more intelligent than most adults give them credit for (frankly, I find most adults to be horrifically insulting to children), I am not sure if all of the concepts and structures used in D&D should be that easily explained to someone that young.
You....do realize that middle school doesn't start until at the earliest 6th grade, which is roughly age 11-12, right? Three years is an eternity in childhood development.
If our standard is genuinely people who have just started 3rd grade, yes, I do think it is a bad thing. D&D players need to be able to handle probability, multi-digit multiplications, fractions, and (usually) areas and perimeters, which are concepts that a freshly-minted 3rd grader has not learned yet. It is not fair to ask a child to learn foundational mathematics they haven't even been taught just to be able to play; it isn't fair to them and it isn't fair to older players they need to play alongside. Especially since I would really prefer the child have at least some idea of variables and elementary algebra, which wouldn't be taught to them for another ~3 years at least.
Some 3rd graders will be precocious or fast enough on the uptake to handle it, and thus this (as it always should be) must be done on a case-by-case basis. But a majority of them simply won't have the background for it yet. If the given age had been 10 or 12 (which is much more appropriate for "middle school" students, as Parmandur originally described...), you would hear far less pushback from me. A 12-year-old should generally be equipped with the math background to actually play D&D without needing to be taught how to do the math involved. A 10-year-old is probably proficient, or close enough that only minor guidance will be required (as I said, kids are a lot smarter than most adults give them credit for), so it shouldn't be too difficult.
"Hard and fast" relative to what? Because your other statements seem to indicate it performed just as well as, if not better than, prior editions. If you perform just as well as every other edition except 5e, can it really be called falling "hard and fast"?
Which, again, could be due to a host of things that have nothing to do with 5e's contents. Nor, to be clear, with 4e's contents. I am not saying making 5e more like 4e would automatically make it more well-liked. I am instead suggesting that there are parts of 5e which are not helping (or potentially even hindering) its outreach, and which would have been changed by its designers before launch if they knew what the future held.
Based on the graphs recently put out, even 1e had that, it just maybe lasted a year or two longer. So...is 4e some special failure that needs to be highlighted, as I know you have argued in the past, or is it the same as every prior edition and only 5e has played out differently?
Though it's worth noting, PF only overtook 4e when 4e stopped putting out as many new books. It only really overtook things when 4e pretty much stopped printing anything at all; keep in mind, 4e basically stopped publishing well before the D&D Next playtest was announced. Almost all of 4e's library was published between 2008 and 2010: only four books were published in 2011, and only two in 2012. Now, obviously there are major differences between 4e and 5e in terms of publications, both number and intended impact (only people who wanted to play Divine characters wanted Divine Power, for example), but the point stands, PF overtook 4e because the latter stopped making books. It's pretty easy to beat the sales of something that isn't making new product, and PF1e launched in 2009...and took 2-3 years to overtake 4e. Imagine that.
Wait, wait, just to make sure I understand you here. You're saying Thor should be a spellcaster. One whose primary ability score is Wisdom. And that Aquaman, who can psionically control underwater life, should be a Champion Fighter. Like I'm not even going to touch how Megumin absolutely isn't an Evoker (which gets class features for being more careful about explosions...) The previous criticisms are damning in and of themselves.
Which would be 2011. Exactly when 4e reduced its publication schedule by more than half, and then only published two books thereafter.
Well, it would help if people recognized, y'know, more of reality, like the above, and didn't repeatedly say that 4e was a massive failure in order to justify crapping on literally absolutely everything they can about it.