> It seems controversial that Congress could create independent executive agencies.

To whom? The U.S. Constitution says that Congress has the power

"To make all Laws which shall be necessary and proper for carrying into Execution the foregoing Powers, and all other Powers vested by this Constitution in the Government of the United States, or in any Department or Officer thereof."

That's rather clear.

The legislative branch makes those laws and the executive branch executes them. Beyond that its role is limited ... commander-in-chief of the military, pardon power, making treaties (with approval of the legislature), appointing ambassadors, judges, and other officers (with approval of the legislature).

The legislature creates (or removes) the departments and sets forth their duties. The role of the executive is to see to it that the departments carry out those duties as established by the legislature.

The "unitary executive" is not to be found in the U.S. Constitution ... it's a creation of authoritarians.