The court cases are complex and merely listing them doesn't offer anything useful. Second, it's an appeal to authority.

You don't provide any info about the cases, cite any relevant passages, or make a case for why you think the rulings were correct.

But let's address the management clause. It doesn't bestow any right on the federal government to own property beyond that necessary and proper to carry out its enumerated powers. Obviously, there's an interim period between cession and disposal that management is necessary. But disposal is still required.

As stated in M'Cullough v. Maryland, 17 U.S. (4 Wheat) 316, 422 (1819) "The power to 'make all needful rules and regulations respecting the territory or other property belonging to the United States,' is not more comprehensive than the power 'to make all laws which shall be necessary and proper for carrying into execution' the powers of the government."