If they were made by the same race, I wonder if it were possible for them to procreate? What would oneo f thier offspring be like? Either way, that actually seems like a decent idea, Apple. Ep would make the best cook anyhow, due to their amping magic.
As for the race distrubution, in the
Five Races model the EP's would be stout, and the Pegais probably High Men - elves. The unicorns are more akin to Fey.
Of course, Tolkein didn't have an analogue for the Fey, so... Actually all things considered in terms of racial culture, the split is more like Pegasi = Dwarves(Agressive, hardy and boistrous. In general), Unicorns = Elves(Aloof, Magical, slightly pompous) and Earth Ponies = Hobbits(Simple, pleasent, content to farm the land). At least, going by the Hearth's Warming tribes. By the time the series roll around things are much more cosmopolitan.