Earlier quoted context omitted.
Except that's a bad summary of a bad argument. "Rulemaking" is what Congress is supposed to do .
The Constitution doesn't say that Congress can have its employees (which is what the Copyright Office is) make legally binding rules. Congress can make laws, but only through a specific process involving votes in the House and Senate and the signature of the President.
Your initial comment would have been far stronger if it had dropped the irrelevant ad hom I called out previously, and had clearly stated your concern with Congress both legislating and regulating copyright, through the Library of Congress.
This also makes the question of how the Library of Congress came to be empowered with executing and* regulating copyright of interest. You've failed to explore this history. I'm somewhat familiar with both copyright law and the history of the Library, though not as a lawyer, and not specifically on the history of copyright and the Library both being effectively an executive function of the Legislative.
That also makes me wonder what other cross-branch functional contradictions exist. One that comes to mind immediately are ALJs (administrative law judges), which operate under the Executive rather than Judiciary, with one notable area being immigration law. The Senate and House each have Seargents of Arms, a nominally executive law-enforcement role under the legislative.
And of course there's the question of the present Administration's view that not only is it a unitary executive, but apparently a unitary Legislative and Judiciary as well.