There is the text of the ruling that goes into detail about what constitutes a recess vs. THE recess. What’s an adjournment and what’s a session. They say the constitution was written at a time when Congress could go months without being in session. I hardly think that just because Congress doesn’t convene for 3 days means that it’s in recess. If the office has been vacant for 3 years like in your example, there’s no excuse for making an appointment during a recess. Presidents have been abusing the recess appointment thing for decades.
Your point conforms with the plain language and original intent of the Constitution. The recess appointment was designed as a temporary measure to allow continuity of the government at times when the Senate was not available to consider appointments. It was not designed to get around the confirmation process or to allow the President to act unilaterally when the Senate refused to do as he wanted.
One of the major problems with contemporary society as well as modern government is our tendency to place a greater value on finding and exploiting loopholes than on accepting and complying with established rules even if we don't like them. The current administration is taking contempt for established order to a new high.