The Isaiah text backfires because just as Eliakim will fail, so will the papacy as this proof text goes.
20 "In that day I will summon my servant, Eliakim son of Hilkiah. 21 I will clothe him with your robe and fasten your sash around him and hand your authority over to him. He will be a father to those who live in Jerusalem and to the house of Judah. 22 I will place on his shoulder the key to the house of David; what he opens no one can shut, and what he shuts no one can open. 23 I will drive him like a peg into a firm place; he will be a seat [a] of honor for the house of his father. 24 All the glory of his family will hang on him: its offspring and offshoots—all its lesser vessels, from the bowls to all the jars.
25 “In that day,” declares the LORD Almighty, “the peg driven into the firm place will give way; it will be sheared off and will fall, and the load hanging on it will be cut down.” The LORD has spoken.
As for the Revelation referrences, they refer to Jesus alone as having the keys.
Revelation 1:18
I am the Living One; I was dead, and behold I am alive for ever and ever! And I hold the keys of death and Hades.
Revelation 3:7
To the Church in Philadelphia ] "To the angel of the church in Philadelphia write:These are the words of him who is holy and true, who holds the key of David. What he opens no one can shut, and what he shuts no one can open.
This text may be a better starting point,
Isaiah 51
1 "Listen to me, you who pursue righteousness
and who seek the LORD :
Look to the rock from which you were cut
and to the quarry from which you were hewn;
2 look to Abraham, your father,
and to Sarah, who gave you birth.
When I called him he was but one,
and I blessed him and made him many.
Eph 2:20
But, if he has read any of the church fathers, then he will know that the sheppard teaches that the Son of God is the Rock that the church was founded on.
I was you, I would emphasize Eph 2:20