What are different democracies people believe in?
Simplified, the President executes laws written by Congress via the Executive branch. Congress passes laws that must agree with the US Constitution. The Judicial branch arbitrates disputes by interpreting the US Constitution. The Constitution can be changed per Article V.
Yeah: The guy who said he could shoot someone on Fifth Avenue and not lose any votes. That guy. Who wasn't elected absolute monarch, no matter what the unitary-executive crowd fondly believes.
Trump isn’t governing like a monarch. He’s not regulating private conduct or imposing taxes or putting people in prison. What he’s doing is exercising the executive power, as vested in him by Article II.
(As an aside, Article II says what it says. We don’t need a label for it. What requires a label is the theory that there’s an independent civil service insulated from the President and political appointees.)
The "executive power" is what's enumerated in Article II — most notably the All Other Officers Clause and the Take Care Clause. (It's been often said that it was no accident that the Framers put Article I first.)
So: If both houses of Congress pass a bill saying that Agency X is insulated from the president and political oversight — and the president signs the bill into law — then that should be the complete and utter end of the discussion until Congress and the president agree to change the law.
Those folks who've been bootstrapping a unitary-executive monarchy are engaging in ... let's just say, "creative lawyering" (spelled: making it up out of whole cloth). At least Marbury v. Madison has some policy grounds underlying it (the least dangerous branch and all that); the unitary-executive fantasy is devoid of such advantages.
BTW, just because Trump hasn't yet done all the things a monarchist could do, doesn't mean he's not a monarchist; saying otherwise is atrociously illogical.