The fact that they are all apparently scanned off real people probably tells you something about the diversity level in the office lol.
If it was handled via sliders, this would mainly come down to controlling the height of the bridge of the nose, since that is what creates the epicanthic fold around the eyes in an actual human skull. The next most important slider would be for controlling cheekbone height.
They're probably not going to get at the levels of diversity desired by just scanning, unless they are scanning like hundreds of heads. Which they could also do I suppose. But it seems like it'd be simpler to start with basic skull shapes, or at least try find models that demonstrate more of the variety we see out in the world. So they don't end up exacerbating the issue by scanning in a bunch of real heads that just end up looking essentially the same as what they already have. Everything vaguely described with reference to geography or race is better understood with reference to the human skeleton and skull. Sure cephalometry isn't like a real deal science, but its useful for artists and illustrators. Associating the skeleton/skull or facial features in general with ethnicity or race is pretty sketchy territory and has a very fraught history. Its easier to talk about it in terms of abstract structures like just the basic shapes of the bones where the cartilage attaches, more the way its done in forensic anthropology. Since that's what's really going on anyway.
To be specific, what is missing from the female elves right now would be more skulls with a wider nasal aperture=lower bridge, more distinctly rectangular or circular shaped orbits, wider set jaws=lower cheekbones, and more variety in the shape/width of the teeth. Which is just another way to say that simply adding more hairstyles or darker colors to the skin tone palette isn't exactly doing the trick hehe.
One of the reasons facial sliders usually suck in other games is because they don't take into consideration how features relate to each other and the underlying structure, but instead treat them all independently like its Mr Potato head.
The various/diverse facial features we recognize that aren't just melanin on the surface are mostly down to the skull. The female elf skulls right now all have what would be called "European" skull features, at least by 19th century standards. Narrow nasal apertures, aviator orbits, and narrow jaws=high cheekbones. You know, like its Vogue magazine (for most of its history), just with really long and pointy ears hehe.
If scanning real people, would be nice to see them put in a bit more effort during the next round of casting calls.