5. It was not controlled for the positions of choices in the menus, that has an effect on what people choose.
Barbarian, Bard, and Cleric are at the top of the menu, but they're kinda spread out in the rankings.
Other than that, yeah, all factors.
I think WAY TO MUCH is being made of that data dump and article.
My feeling is that it's like one of those studies that confirms the obvious. It may or may not be a good study, but it's easy to accept the conclusion, because it's, well, obvious.
Tony Vargas (a fellow lifer) probably has the same experiences as me.
Fighters were the choice in 1e (best chance to survive) were just ok in 2e, were ok in 3e but really good when the Warblade and stuff came out, were really good in 4e, and are just ok in 5e.
I think you're using 'good' here in the sense of effective or capable in some sense (you mention survival, for instance)? Once TWF & double-specialization became options, the fighter had an 'optimal DPR build' (long before that was a thing), so the 2e and late-1e fighters were powerhouses in that area. IMHO, the 5e fighter returns to that, it's just by a narrower margin, and shares the high-DPR laurels with several other classes, I guess it's also slower-maturing. The 3e fighter also had a couple of high-power builds that were arguably viable, or at least occasionally relevant, in spite of CoDzilla, but was, overall Tier 5, & the 4e fighter had the privilege of being a well-supported 'Defender' in a generally better-balanced iteration of the game. :shrug:
OTOH, the fighter design has gone from simplistic, to broken, to elegant, to specialized, to ...derivative, I think, is the only way to describe it succinctly. It's gone from toughness, to DPR, to customizeability, to defense-of-others, and back to DPR again. It's gone from balanced-by-items, to broken by optional rules, to optimizeable, to solidly supported in one role, to.
In Tier terms, even though they were invented specifically for 3.5, the fighter's roughly gone from Tier 5, to Tier 4, to Tier 5 (the only really valid data point in this chain), to Tier 3, to Tier 4.
It's been all over the map in a lot of ways, but it's consistently remained the most popular class. Same with human, though it's bounced around less, it's still consistently most popular.
It just dosn't seem plausible that you'd get consistent popularity from wildly varying roles, mechanics, support, balance, etc...
Thus, my conclusion is that Fighter and Human are popular because of an understandable preference for concepts that just don't fit into other classes or races. Familiar and/or relatable and/or prevalent-in-genre concepts.