Derived authority allows people to exercise such authority...the power to bind and loose, the power to forgive sins.
It doesn't mean that the One from whom such authority is derived ever lost it.
Likewise, Paul twice references Jesus as THE Head of the Church.
No undivinated man is the head of the Church; Jesus never abdicated that role. He is STILL Head of the church.
The point is that the Church is his vehicle to share the Gospel to the world. The Apostles are who God has chosen to work through.
Their authority stems from Christ - if Christ no longer had authority neither would they. The alternative is also true - remember what Christ said to the centurion? The centurion told Jesus- “command it and it shall be done, just like the centurion commanded his soldiers - Christ would command his disciples. “you tell them Go and it shall be done.”
Rejecting the authority of the Apostles is rejecting Christ’s authority.