It is much worse than just creating a legislative branch under the executive. Executive agencies are judge, jury, and executioner when it comes to their rules. They have their own enforcement teams, courts, and make up their own penalties for violating the rules they made up. They are like a government inside the Constitutional government.

The government is required to give everybody a speedy trial with a jury of their peers. Fines are also required to not be excessive. Violate an executive agency rule and you will not get what is required by the Constitution.