Would still like to know how mankind deviated into so many different variants

[Kakurady]

The Hyur are also omnipresent across the entire planet in a way the other races are not, including in the New World, which seems to indicate them previously having been the dominant species of the world. Though, that's of course a post-hoc justification. The real reason is that they're fantasy humans, and making fantasy humans the generic race that's everywhere is just a thing writers do.

Lore implies Hyurs (like real-world humans) are just really good at long-distance migrating.

In the character creation screen, it says Elezens regard themselves as native to Eorzea, while Hyur are said to have migrated to it from surrounding areas.

Of course, that having happened several eras ago, no-one in universe or out would know how reliable that is.

[Lurina]

Lore implies Hyurs (like real-world humans) are just really good at long-distance migrating.

In the character creation screen, it says Elezens regard themselves as native to Eorzea, while Hyur are said to have migrated to it from surrounding areas.

Of course, that having happened several eras ago, no-one in universe or out would know how reliable that is.

Despite the Elezen's outlook, Encylopedia Eorzea says that Hyur have been present on Eorzea since before the First Astral Era.

[MikkoAkure]

Despite the Elezen's outlook, Encylopedia Eorzea says that Hyur have been present on Eorzea since before the First Astral Era.

Yes and no. Hyur obviously lived on Eorzea in previous eras. But after the 6th Calamity the Elezen were first to repopulate Eorzea, followed by the Hyur. The Eorzea Encyclopedia says that the Hyur immigrated to Eorzea in 3 waves, the first one was over 300 years into the 6th Astral Era and was what led to a large group of Elezen leaving the Shroud and creating Ishgard.

In the original 1.0 lore before Yoshi-P, there were no eras and Elezen were always the original natives of Eorzea so they had to reconcile the old lore with "everyone leaves but then they come back because Eorzea has a lot of aether".