Inherited wealth was actually pretty rate in the history of this country, and is not as common now as many people think. Generational wealth until recently did not exist for most people.
Large portions of existing wealth are inherited, most estimates putting it somewhere in the 30-60% range of all private wealth in the US
I don't think that's what people have been taking away from the idea of stereotype threat at all. I think it's been much more likely for people to think, "Oh, instead of unchangeable genetic traits, the difference in outcomes might someday be reduced through deliberate social change.