You, sir, are wrong. The Copyright Clause in the US Constitution is quite short and leaves a lot for Congress to create:
"To promote the Progress of Science and useful Arts, by securing for limited Times to Authors and Inventors the exclusive Right to their respective Writings and Discoveries."
Congress has the power to create the instrument that controls the way patents and copyrights are issued and cancelled. The Constitution only requires that patents and copyrights EXIST, not how they are managed, which IS an Executive Department function, but under the aegis of Congress to establish the laws under which such copyrights and patents are handled by the Executive. That means the statutory law, and the regulations promulgated under it, which you claim has no power to affect patents is the controlling factor, not the courts.
I should have mentioned that the section at issue is Amendment VII rather than Article I Section 8. Amendment VII grants the courts their supremacy, it’s more about who gets to make the decisions rather than a patent issue per se. The Supremes struck down a similar agency encroaching on the court’s prerogative so it will be a surprise if they don’t slap down the PTAB as well. Although predicting court behavior is a risky business.