I think Barr gave us the answer to your question in his speech to the Federalists:
” As of September of this year, the Senate had been forced to invoke cloture on 236 Trump nominees — each of those representing its own massive consumption of legislative time meant only to delay an inevitable confirmation. How many times was cloture invoked on nominees during President Obama’s first term? 17 times. The Second President Bush’s first term? Four times. It is reasonable to wonder whether a future President will actually be able to form a functioning administration if his or her party does not hold the Senate.”
By stalling approval of Trump nominees, Congress has forced Trump to leave Zero appointees in place.
I don’t agree. He could have fired them all and put in actings and if the time limits on the acting runs out, he could have changed actings or used deputies, etc. That is what White House personnel is for if it is controlled by the President’s loyalists. Sure it can be difficult, but not as difficult as leaving the enemy in so many key positions.