I (try to) view the editions as something of a continuum. 1e had no really useful rules for item creation. 3e did. That the 3e rules aren't in 5e tells me that experiment - for such it was - didn't work out very well; and so they've gone back to plan A.I view every edition as stand-alone. For example I don't assume that just because 5E doesn't have rules for creating magic items, the 3.5 rules for creating magic items becomes the default.
That's a new one on me: where does it say the minimum (natural) ability score is 1?The basic assumption that ability scores are based on a 3d6 bell curve is not part of the game. The rules currently only assume is that the average commoner has around a 10 ability score, the minimum ability score is 1, the maximum is 18 with some exceptional individuals getting up to 20 (for most humanoid/NPC races).
All our other disagreements here notwithstanding, the tighter-bell-curve assumption you're using is bang on. It's still a bell curve, which is a huge improvement on the 5e suggestion that all NPCs have 10s in everything, but not as loose or extremes-heavy as 3d6. Perfect!Beyond that the DM is free to make whatever assumptions they want based on the style of game they want to play and how they envision their world working. For example, I assume a bell curve as well, just one that is far more clustered around the average than 3d6.
But how to achieve the tighter curve using dice, is the question?