John 20:21-23 is a post-resurrection quote from Jesus saying much the same thing as the post-resurection quotes in the other gospels. The disciples were to receive the Holy Spirit, be sent out as Jesus' agents, and baptize people to remit their sins. Protestants don't normally say the Great Commision applies only to apostalic successors or priests. All Christians are agents of Christ, doing everything in his name.
I don't see any reason to limit what Paul said in the 2 Cor passages to apostles or priests. We are all entrusted with the message of reconciliation. John in his letter, I John, tells the readers to pray for a brother they see committing a sin and the brother will be forgiven. John did not limit this to power to apostles or to those holding a church office.