But, the races distribution is basically the top 5 and then everyone else.
That would be true if and only if that top 5 were immutable and
half-orcs didn't make it into the top 5 in 2020, pushing out elves. Clearly it's not "the top 5 and then everyone else" when the second lowest ranked PHB race in 2017 makes it into the top 5 in 2020 and two of the races in the top 5 in 2017 (dwarves and elves) don't make it in in 2020.
That says to me that the "everyone else" needs some work because it's certainly not very appealing to players. It's not 1974 anymore. There's no reason we have to have our "base races" modeled after Lord of the Rings. If any race isn't really making the cut, then, well, it's time to try something else.
There's "a race" and there's "masses of races". I have never suggested that changing races one by one was always terrible. I'm simply saying that you want to use a scalpel not a chainsaw and halflings are not the race most likely to be cut.
I mean,
@Neonchameleon talked about how there aren't other races nipping at the heels. I disagree. Even by that table, Aaracockra and Aasimar both look to have a decent shot.
You missed Genasi. Who would be a better example.
But the simple fact is that
none of those races are nipping at the heels of halflings. 2.9% isn't nipping at the heels of 4.7% They wouldn't even be doing so if they were more popular than halflings because they are not in any reasonable way like halflings. If we replace halflings and gnomes with aasimar and genasi the game becomes smaller because although genasi and aasimar cover
some concepts better than existing races they are strongly overlapping with high elves and tieflings. Meanwhile you are proposing cutting out halflings and gnomes at the same time.
If it's decided that subraces are a mistake then putting genasi or even aasimar into the PHB as high elves makes 100% sense. It's what 4e did with Eladrin after all.
A flying race in the PHB would be outstanding.
A flying race in the PHB would certainly stand out - in making entire adventures irrelevant, in encouraging splitting the party (because some can fly and others can't) and in making it harder for DMs and especially new ones. Especially at level 1. Even Tasha's only hands it out fairly widely at level 6.
Free access to flying does not belong in the PHB at level 1. And if it doesn't belong there either you need to make the flying races only glide at low levels (which adds complexity so doesn't belong in the PHB) or you need it in supplemental material.
That said I'd be fine with a feat for giving dragonborn, aaracokra, and even aasimar functional wings.
But, again, since halflings are down at the bottom of the barrel, and always have been, right from the word go back in 1974, maybe, just maybe it might be time to give something else a try?
All the evidence presented says that halflings are not at the bottom of the barrel. They're ahead of gnomes and as far as I'm aware always have been.
The only reason we're having this discussion at all is the Gnome Effect. Removing halflings might impact up to 25% of tables, so, that's a large enough number that we have to keep them in, even though they are basically just dead weight. Exactly the same conversations we had in 4e when they pulled gnomes.
And of course they reversed that.
But that was a single cut at the bottom. You're suggesting going in with a flamethrower and burning multiple races in one fell swoop. If removing just
one PHB race had that effect, and the least popular PHB race at that, what on earth do you think removing several will do?