Of course Paul is intrinsically unnecessary for our redemption or the created world, you silly wabbit! God could have used "Irving" to make known the truths of the gospel to his embryonic church. He chose Saul (Paul) and therefore the words he spoke are recorded in the Bible and accepted as the revealed words of God - as God willed. By the same token, God could have chosen a young virgin named Hannah instead of Mary to bear the Savior.
I totally agree that without Jesus Christ, Paul's words would mean nothing, but the entire Bible is about him so he is, of course, its center. Without him, not one word would make sense.
The Epistle of St. Irving to the Romans? I remember when I was a new convert hearing a very nervous lector announce "A reading from the letter of St. Paul to the Filipinos". Oh that cracked me up.
Would "The Apostle Irving" have written different epistles? The same doctrine would have been communicated to us but in a different way, wouldn't it? Surely his personality would have been his own, Paul's writing style is different than John's for instance so it seems something of the writer shines through.
In the same way suppose it had been "The Blessed Virgin Hannah"... the same Christ would have been born... but would there have been ANY differences?