I don't know enough about Nietzsche to say, really. Sartre's my real target anyway. Sartre believes that "existence is prior to essence". If I recall, he even made that the foundation of the word "existentialism". Sartre's "existence is prior" is French-philosopher-code for "we have contra-causal free will." And that's not just incidental to his views on morality, whereby he accuses moral realists and cognitivists of "bad faith". It's absolutely central, because without that alleged ex nihilo freedom, we couldn't create values in the way Sartre says we must. And we wouldn't (don't) need to create values ex nihilo. We could (can) study our essential human qualities, and figure out what makes us flourish or suffer.