I know that nucleophilicity order depends on what type of solvent we take, polar protic or polar aprotic and also on the basicity of nucleophile.

In DMF, which is a better nucleophile $\ce{NH2-}$ or $\ce{OH^-?}$

Since the solvent is aprotic polar, it doesn't have any donor hydrogen to form hydrogen bonds with nucleophile. So, the nucleophilicity should depend on which among them is more basic. Now, since $\ce{N}$ is less electronegative than $\ce{O}$, it's lone pair is more readily available than that of $\ce{OH-}$.

So, according to me, $\ce{NH2-}$ should be more nucleophilic than $\ce{OH-}$, but the answer given is the opposite, that is, $\ce{OH-}$ is more nucleophilic than $\ce{NH2}$-. How is my reasoning incorrect?

And also what are the factors we should keep in mind while deciding nucleophilicity?