Not exclusive. Mt. 16:19 does not say "unto thee and thee alone." Speaking to all disciples a bit later, recorded in Mt. 18:18, Jesus said, "Verily I say unto you, Whatsoever ye shall bind on earth shall be bound in heaven: and whatsoever ye shall loose on earth shall be loosed in heaven." You is plural in the Greek and in the English.
Bringing that forward, anyone now knowing the essence of The Faith can use It--the Gospel, the keys--to point to the Open Door to the Kingdom of Heaven, the visible church.
Peter used them once, on Pentecost, for the Jews; and once later, for the Gentiles.
However, Jesus' Kingdom, the Kingdom of God, is not of this world (Jn. 18:36), and nobody but Jesus has the key to that Kingdom. He is the Way, The Tuth, the Life, and the Door to that Kingdom. Peter has no control over who enters the Kingdom of God.
...Matthew 28:18-20
18 And Jesus came up and spoke to them, saying, "All authority has been given to Me in heaven and on earth. 19 "Go therefore and make disciples of all the nations, baptizing them in the name of the Father and the Son and the Holy Spirit, 20 teaching them to observe all that I commanded you; and lo, I am with you always, even to the end of the age."
It does NOT say ANYTHING about all the EXTRA junk that Rome has come up with!!!
It doesn't say NOT to; so THERE!
Catholic_Wannabe_Dude(HailMary!! These Prots just do NOT get it; do they; Mom!)