The Constitution guarantees the States a republican form of government. If the Tenth Amendment is void, then there is no republic and that guaranteed has not been honored. The contract is broken, and Congress has no legitimate authority at all.
They may have no authority but they do have a fair amount of Power and a tyrant that is willing to use it.
The Constitution is about as useful as an order of protection against an abusive husband intent on murder, the wife can wave it in his face while he chokes the life out of her. Maybe she should have a gun permit to wave instead.