Where does the Constitution EXPLICITLY forbid the president from suspending the Writ?
Foul! Irrelevant conclusion: the argument you assert for presidential prerogative is a misapplication of the argument about reservation of powers. The secessionists argued that the right of secession is among the rights reserved by the Ninth Amendment explicitly, and by the body of the Constitution implicitly because the Constitution doesn't delegate to the federal government any power to forbid secession.
The President has no power that is not delegated to him by the Constitution.
Nope. Please. Where does the word "secession" appear in the document?
What is EXPLICITLY stated in the Constitution is that the laws of the federal government are supreme over all state laws. Nothing in a state law can withstand the supremacy clause.
It is just as reasonable to ask where the Constitution forbids the executive to suspend the Writ as it to ask where it forbids secession.
You can't have it both ways.
Walt