Two points. First, Congress can 'reserve' absolutely nothing - it was a party to neither the Articles nor the Constitution. Any powers possessed by Congress were delegated by the States, and Congress possesses absolutely no power that was not so delegated.
Second, to imply that Dr. Amar advocates your 'anything the court says is constitutional' position is utter hogwash. Dr. Amar has observed that:
"The careful reader will no doubt notice that judges are not exactly the heroes and heroines of my tale. Federal judges, after all, enthusiastically enforced the infamous Sedition Act of 1798, cheerfully sending men to prison [for simply criticizing the President] and neutering juries along the way. It is hard to imagine a bigger betrayal of the Bill of Rights..."
Akhil Reed Amar, The Bill of Rights, 1998
Looks like you're not a "careful reader" (no surprise there, given the fact that you missed both of my posts answering the question you posed earlier ;>).
Dr. Amar, by the way, also suggests that Mr. Lincoln's draft was entirely unconstitutional.
;>)
One of those powers is the the power to change the status of a state.
ROTFLMAO! As I noted earlier, your suggestion that the federal government may eliminate or expel a State is a 'nonsequitur' - it is a "conclusion that does not follow from the premises." If your reasoning were correct, the power to create a child would somehow endow parents with the power to kill a child. That, quite obviously, is incorrect.
(Perhaps you should select a different 'screen name' - it applies to too many of your posts! LOL! ;>)
Perhaps you should adopt it?