First off, the conversation I think I was having, with others - not you; was about people seeming to need explicit language in the rules to do stuff like forbid non human pcs in their campaign or whatever. Which, is counter to the ruling not rules ethos of the game and is a very 3.x RAW is King view of the game.
Secondly, I think it was ever thus, with regard to the diversity of playstyles, that D&D has been asked to service. With the exception of 4e and possibly in a different way Basic, D&D has not been very focused.
While I agree that 4e was very focused and clear as to what it was striving to be, I do not accept that 5e is not well designed. I think it is pretty good. I may have preferred 4e a few years ago I am increasingly impressed by the robustness of the 5e game.
Aside from that, however, 4e was commercially not as successful and 5e is a much more commercially successful game. Given that WoTC/Hasbro are looking to profit from D&D IP in the broader entertainment world, they have every incentive not to alienate any part of the market. So they would see broad appeal and lack of focus as a selling point and a marketing bonus.
I played back in those days, (though not with Dave or Gary) and my experience was that D&D followed lineages based on the DM and player that introduced players to D&D in an area.
I played many of those old Avalon Hill games back in the day and those rating systems were highly hit and miss.