You have no understanding of the Constitution, whatsoever. If what you say were so then the Constitution is meaningless; there are no rights, only privileges, and any judge, through any process, could strip you of your rights. And, in fact, in no jury trial was any defendant notified that their right to keep and bear arms were being tried and in no sentencing ever, did any judge tell a defendant that their right to keep and bear arms was revoked - so even by your illegitimate understanding of due process, there was no due process. The entire meaning of due process, going back to the Magna Carte, was that a person was notified and able to defend their rights.
But, you're assigning to due process the power for the government to do things not already permitted in the Constitution. As long as a court rules that a person no longer has the right to a trial by jury, then can the court sentence someone to life in prison without a jury trial?
But even this ridiculous example would offer more protection than you're suggesting due process offers. By your example, there would not even be a hearing to say that the right to a trial was stripped, the judge could simply go straight from indictment to sentencing.
To make this stripping of the right to trial match the scenario that you say gives the government the right to strip someone's right to keep and bear arms, all that would need to be done is for Congress to pass a bill that says convicted felons no longer have the right to a trial by jury or the right to legal representation, or the right to a speedy trial. Congress could take away all rights, 1st, 2nd, 4th, 5th, 6th, 8th, Amendments gone.
In fact, why can't Congress create a law stripping the right to due process on conviction of a crime? And if they can do it based on conviction of a crime, why can't they do it based on accusation of a crime? Or based on skin color or religion?
So, please make it clear, you're making the claim that the Congress can take any right from any person for any reason by passing a bill that says they can do it. Correct?