> Drawing categorical lines is legislative.

That’s even worse. If that’s the case, Congress must adopt those exemptions by law. It can’t delegate lawmaking powers to its employees.

> Stepping back, both doctrines (non delegation, unitary executive) are fundamentally about the courts overstepping

Unless you toss out the concept of judicial review altogether, policing the structural rules of the constitution is exactly what the courts should be doing. The courts have no say about the merits of Congressional acts. But they should review whether Congress has allocated powers to various entities in a way that’s consistent with separation of powers.