Which by my reckoning will start in 2061 at the earliest. We've had 40 years of using them a decent amount at tables.
This is a false dichotomy based on not looking at what is actually being said.
Halflings have 100% of the lore they need for a race in the PHB. They are completely fine there. And there is so far as I can see no good argument for removing them from the PHB other than that they are not one of the cool kids and you want to take a hatchet to the PHB, removing at least a quarter and possibly a full third of the races depending on how half-orcs are doing this year.
They are also, so far as I can tell, seriously short-changed in both the lore of the Forgotten Realms and the lore of Greyhawk so far as I can tell. And they aren't even in Dragonlance at all that I recall (no, Kender aren't Halflings). If you are right about 5e adventures they are short-changed there (the only official 5e adventure I own is Curse of Strahd) - and even if you aren't right, assuming you were reading in good faith they are easy to overlook.
I've never been inspired by anything I've seen out of the Forgotten Realms and think I only own one Realms sourcebook (4e Neverwinter) - but this doesn't somehow change the fact that the Realms was the default setting for 2e, 3.X, and 5e and there is a ludicrous number of sourcebooks for the Realms. It also doesn't change the fact that Greyhawk was the dominant setting in the 3.0 PHB and the default setting back in 1e. And it doesn't change the fact that Dragonlance through at least the 80s and 90s and probably right up until 2004 with Eberron was at least the third and probably for most of the time the second biggest setting in D&D.
To give other examples of how they were short-changed, 2e had a complete book each of humans, elves, and dwarves - and a complete book of gnomes and halflings. The 3.5 racial guides also had the human fronted races of destiny, the elf fronted races of the wild, and the dwarf fronted races of stone - and the dragonborn fronted races of the dragon. Halflings were second in Races of the Wild, Gnomes in Races of Stone.
I do actually wonder whether there's a difference here and those of us who homebrew and work from the PHB outwards think halflings are fine - because they are there. But people who regularly use the big published settings see the lack of care paid to them.
It also casts light on your attempt to remove halflings from the PHB (where they are fine) to the DMG being your attempt to remove the parts that are actually working.
What you can do is start looking at nuances and stop with the motivated reasoning. We aren't a hivemind.
But you have done nothing to respond to points about the knock-on effect of removing the lowest performing race and the impact that will have on halflings. You've done nothing to respond to the point that if you break things down by subrace and apply your crude filter we kick out dwarves.
And you can start responding to the point that neither Tieflings nor Dragonborn came out of nowhere. It seems that you ignore all the points that go against you unless you can find something to nitpick in an attempt to say other people aren't a hivemind.
Now I wouldn't mind this so much if it were a tacit admission that your "points" simply didn't hold water. But you then repeat those debunked points.
I think this is a great breakdown, but I want to take this a bit further and take a bit of a different angle.
Humans, Elves and Dwarves are in the Basic Rules as one of the Cour Four races. They are in the PHB as one of the common races because of this. They have good lore in Forgotten Realms, Greyhawk, Dragonlance, Eberron and somewhat in Darksun (Dwarves were genocided, but the rest are there). In 2e there was the complete book of humans, complete book of elves, and complete book of Dwarves. 3.5 humans were the key race in Races of Destiny, Elves in Races of the Wild, Dwarves in Races of Stone.
All of this leads to them having a massive prescence in the game.
Halflings do not have good lore in Greyhawk or Forgotten Realms. You propose they don't exist in Dragonlance, and they are radically altered for Darksun and Eberron. So, 2/5 of the settings. In 2e they had to share a Complete book. In 3.5 they were second string in the Races of the Wilds. They are still in the Basic rules as one of the Cour Four races, and in the PHB as a common race to reflect this.
And this is the problem we are pointing out. You seem to have taken the stance that "the PHB is fine, because the PHB lore is supposed to be the weakest part" which... is true? I can agree with that much at least, but in my opinion you can't just change the lore outside of the PHB to address this, you need to hook those changes in the PHB, so that the other sources can expand on them.
Basically, if the PHB is the starting point for all of the other lore, then changing that helps change the further lore that follows. It has to flow from the PHB to have the right level of impact. And it doesn't have to be a massive change. Some pretty small changes give us what we need to hook further lore into for later books.