Not all Elezen. Duskwight and Wildwood only exist among Gridainian Elezen. Ishgardian and Sharlayan Elezen are just Elezen. Ishgard is isolationist, hence their shyness around outsiders. It doesn't matter what race someone is, what mattered is you were Ishgardian or Coerthan. The superiority comes from the Nobility, Even be it Hyuran or Roegadyn Ishgardian Nobility (yes there are both) There are Hyur, Miqo'te, Roe, Lalafellen etc Ishgardians. Gridanian and Ishgardian founded within about 100 years of one another. Eorzean Elezen do not know why they have the naming system they do as they do not speak anything other than 'common'
Not quite true: there are a number of Duskwights in Sharlayan. Whether they have migrated there or their Duskwight great-grandparents did doesnt really matter, but they are there.
I've played Elezen since 1.0. I've never noticed they don't move their arms and legs. I rather prefer a nice posture. They just don't waste movement, they have no need to.