I recently got into an impromptu debate with a couple of Catholics on Facebook. I'll post some highlights of what I said in response to what they said.
If Christ forgives through priestly absolution, then a priest has the power to compel Christ to forgive anyone the priest absolves.
John 20:19-23 would prove to be problematic for you then. Christ breathed on the Apostles and gave them the authority to forgive and retain sin (if it were merely to announce forgiveness of sin, then it would make no sense to also confer the capacity to retain).
i) Depends on the scope of your claim. That's certainly not a Catholic prooftext, since it's about the apostles in general, and not about Peter in particular. Likewise, it's not about the papacy, or Roman episcopate, or Catholic priesthood, but just about the Eleven.
ii) There's also the question of what Jn 20:23 means or implies. Is that a constitutive act?
In context, it arguably has reference to the Apostolic mission. Evangelism. People who believe the Apostolic kerygma will be forgiven; people who spurn it will remain in their sins.
That's consistent with the fact that in the Fourth Gospel, people who believe in Jesus, who exercise faith in his message about his person and work, are forgiven–while those who reject his message stand condemned. That's the basis of salvation or damnation.
To make salvation or damnation contingent on a constitutive act of apostolic absolution (or the absence thereof) posits two different methods of salvation: one through direct faith in the Gospel, the other through auricular confession and absolution.
That's incongruous. Hence, in context, Jn 20:23 shorthand for how people respond to the Apostolic witness about Jesus.
i) It's not self-evident that Mt 16:18 makes Peter the rock. Although that may seem straightforward considered in isolation, the "on this rock" motif was emphatically used by Jesus, in reference to himself, back in Mt 7:24-25. So Mt 16:16 may allude to that.
ii) But assuming it refers to Peter, the formulation isn't exclusive. It doesn't set Peter in contrast to the other disciples. It doesn't say Jesus will build his church on Peter rather than his colleagues. That imports a nonexistent dichotomy into the text.
It's not as if Peter was the only disciple who believed that Jesus was the Messianic Son of God. So that fails to distinguish Peter from his colleagues. That doesn't single out Peter as the unique basis for the church.
iii) As a matter of fact, the NT extends the foundation stone imagery to the Apostolate generally (Rev 21:14), and even beyond the Apostolate to apostles and prophets (Eph 2:20).