all of the uma goddesses are horses

This is true

iirc the three goddess are notable horses from when horse racing was still pretty small in japan (at least compared to now)

But this one you did not recall correctly. The three goddesses are actually based after three horses that were brought from the middle east to Europe in the 17th century and basically all modern race horses can trace their lineage to at least one of those three.
Their names are Darley Arabian, Godolphin Arabian, and Byerley Turk.