Hiya!
So back the original point is that overall I feel that Humans should not be the only race with diversity as its thing. Despite whatever the origins of Elves, Dwarves, Gnomes and Halflings, in core D&D they are now far removed from their mythological Earth origins, so they don't need to be locked in as exclusively European.
Personally, I do feel that Humans should be the only race with 'diversity as a thing'. The reason is that I've always treated Humans as the "Wild Cards of the Multiverse". Look at 1e AD&D, Humans were the ONLY race that could be "any Class". Humans were the ONLY race that could advance to "any Level" in any of the classes. Humans where the ONLY race that could Dual-Class, and the ONLY race that could NOT Multi-Class. That was the "Human thing"...diversity and adaptability. Remove that, and you are at the "why play a Human then?...", with the only reason being "because I feel like it". Which is fine and all that, but if you're running a campaign and see 20 characters over two years...and 19 of them are non-human, yet, somehow, miraculously, the VAST majority of the campaign world is made up of humans...well...kinda kills that suspension of disbelief, doesn't it? It does to me.
Now, talking non-D&D games and there are likely various other reasons for Humans being the "only" race with wide-open diversity/choice. For example, my second favourite fantasy RPG, Powers & Perils, has Alignments. Alignments in P&P are important in that your Alignment can actually determine day-to-day game mechanics and effects (spell casting and magic use being the most obvious). Humans are the ONLY race that is born as a "blank slate"; they can become the most noble of saints, or the most decadent of hedonists, or the most cruel of psycho-murder-hobos. Humans are all born with No Alignment (also called Orientation in P&P). An Elf? Nope. They are born with an Alignment. Dwarves, Faerry, and any other race/monster...same thing, they are born with a permanent, built-in Alignment. You will 'never' have a Chaos Oriented Elf, or a Law Oriented Dwarf, or a Balance Oriented Faerry. Elves, Dwarves and Faerry are ALWAYS of the "Elder" alignment. That said, the Elder alignment is 'fragmented' into 4 more or less conflicting groups...and these groups ideals are at odds with one another; The Sidh, The Kotothi, The Elder and Shamanic Elder...but ALL are still based on "Elder Orientation", which precludes the purity of Law, Balance and Chaos.
Of course, I AM coming at this from a 1e/HM point of view!
When I'm playing 5e though? Or Pathfinder/3.x, etc style fantasy games? Sure. Go for it! Asian Elves, African Dwarves, Arab Halflings, Polynesian Gnomes, Mongolian Half-Orcs...knock yourself out! Why? The 'style' of 3.x games or later are so watered down and "bland" (for lack of a better word), that nobody will notice a thing and nothing you choose is special or unique...or at least won't be perceived that way. Just "Oh, so you're like a Japanese Samurai Elf? What happened to the African Hill Dwarf wizard? Or, wait, that was Dave's character...oh... right, you were thinking of the Native American Gnome Cleric of Zeus. Ok. Whatever...what's your HP's?"
Anytime I hear about "anyone should be able to be anything and chose whatever" all I can think of is Syndrome's quote:
"When everybody's a Super.... no one will be!"
That sums up 3.x+ games over the last 2 decades for me. I'm NOT saying these games aren't fun or that people who prefer them are playing badwrongfun, but they just don't have the same OOMPH! for me. I enjoy 5e, but when I'm playing it, I'm thinking "D&D The Movie", not "Lord of the Rings".
^_^
Paul L. Ming