Elezen are the 2nd most common race from Eorzea after Hyur so it's pretty natural they'd have a high presence. No one complained about or noticed Minfilia, Thancred, and Lyse all being Hyur. Alphinaud and Alisae are Elezen because their grandfather, Louisoix was an Elezen and they wanted to make new characters who connected to the old story. Estinien started as an edgy 1.0 job quest character and somehow got promoted over time from that to MSQ party member and then eventually Scion by virtue of happening to be an existing character with an existing story relating to the Dragonsong War and then after that, having been a prominent and popular character before so they brought him around again. Urianger... I pretend doesn't exist.

The white hair can probably be explained by standard JRPG tropes and the fact that the Scions came from the artist Akihiko Yoshida, who also gave us characters like 2B, 9S, and A2. I think Yoshi-P recognized the white hair being prevalent in an interview.