I daresay he's certainly a better constitutional scholar than you.
The 10th Amendment talks of powers delegated to the United States AND powers prohibited to the states. Powers to approve changes in status were powers delegated to the United States. Actions that had a negative impact on the other states were actions denied to the states. Implied in both of these is unilateral secession.
For an opposing view more eloquent than I could express, here's a presentation to Congress about the Tenth Amendment: Pilon Statement
Also, let's review statements by various Constitution ratification conventions.
South Carolina: "This Convention doth also declare, that no section or paragraph of the said Constitution warrants a construction that the states do not retain every power not expressly relinquished by them, and vested in the general government of the Union.
New York: "That the powers of government may be reassumed by the people whenever it should become necessary to their happiness, that every power, jurisdiction and right which is not by the said Constitution clearly delegated to the Congress of the United States or the departments of the government thereof, remains to the people of the several States, or to their respective State governments, to whom they may have granted the same; and that those clauses in the said Constitution, which declare that Congress shall not have or exercise certain powers, do not imply that Congress is entitled to any powers not given by the said Constitution; but such clauses are to be construed either as exceptions to certain specified powers or as inserted merely for greater caution."
Rhode Island: "That the powers of government may be reassumed by the people, whensoever it shall become necessary to their happiness."
Virginia: "The delegates do, in the name and in behalf of the people of Virginia, declare and make known that the powers granted under the Constitution, being derived from the people of the United States, may be resumed by them whensoever the same shall be perverted to their injury or oppression, and that every power not granted thereby remains with them and at their will."
North Carolina proposed amendment: "1. That each state in the Union shall respectively retain every power, jurisdiction, and right, which is not by this Constitution delegated to the Congress of the United States, or to the departments of the federal government."
Massachusetts proposed amendment: "First, That it be explicitly declared that all Powers not expressly delegated by the aforesaid Constitution are reserved to the several States to be by them exercised."
New Hampshire proposed amendment: "I. That it be explicitly declared that all powers not expressly and particularly delegated by the aforesaid Constitution, are reserved to the several States, to be by them exercised."
What you mean is that his opinion, and the other opininons you posted on what the Constitution means, are more in tune with your opinions. That doesn't mean they're better.
Yes lets. Four of the statements make the assumption that only those powers expressly reserved to Congress or denied to the states. You quoted your Constitutional expert, Jefferson Davis, let me quote mine. Chief Justice John Marshall, certainly no Constitutional slouch himself, wrote: "Among the enumerated powers, we do not find that of establishing a bank or creating a corporation. But there is no phrase in the instrument which, like the articles of confederation, excludes incidental or implied powers; and which requires that everything granted shall be expressly and minutely described. Even the 10th amendment, which was framed for the purpose of quieting the excessive jealousies which had been excited, omits the word "expressly," and declares only that the powers "not delegated to the United States, nor prohibited to the States, are reserved to the States or to the people"; thus leaving the question, whether the particular power which may become the subject of contest has been delegated to the one government, or prohibited to the other, to depend on a fair construction of the whole instrument. The men who drew and adopted this amendment had experienced the embarrassments resulting from the insertion of this word in the articles of confederation, and probably omitted it to avoid those embarrassments. A constitution, to contain an accurate detail of all the subdivisions of which its great powers will admit, and of all the means by which they may be carried into execution, would partake of the prolixity of a legal code, and could scarcely be embraced by the human mind. It would probably never be understood by the public. Its nature, therefore, requires, that only its great outlines should be marked, its important objects designated, and the minor ingredients which compose those objects be deduced from the nature of the objects themselves. That this idea was entertained by the framers of the American constitution, is not only to be inferred from the nature of the instrument, but from the language. Why else were some of the limitations, found in the ninth section of the 1st article, introduced? It is also, in some degree, warranted by their having omitted to use any restrictive term which might prevent its receiving a fair and just interpretation. In considering this question, then, we must never forget that it is a constitution we are expounding."
In three of the cases you mentioned, their wording of the 10th Amendment was not adopted. In South Carolina's statement, their assumption that only expressly listed powers were reserved to Congress or denied to the states was simply wrong.