I don't know, but nothing says that those were the sole powers. If Marshall is correct and interpretations must be made based on a broad reading of the entire Constitution then it makes more sense to think the authors of the Constitution would explicitly state the exceptions rather than leave them to be assumed.
The powers listed are the sole powers. The Constitution sets up a federal government of limited powers; that is, the states granted certain powers to the federal government. If the states didn't grant those powers, then the federal government doesn't have those powers. Thus, if it isn't in the Constitution, then the feds don't have the power.
But look, I don't think I'm going to convince you that you're wrong on this one, so I leave it at this: you've got to ask yourself why the Framers chose to explicitly ban secession in the Articles and then did not do so in version 2.0.
So far as I'm concerned, there is no rational way to explain that fact other than that the Framers made a choice to retain with the states the unilateral power of secession.