While I don't think of Paul as being more authoritative than the Gospels, he certainly points me to the way that scripture and tradition functioned for him in his work establishing and maintaining communities of faith. Gospel writing is such a different genre... almost completely invented in the Gospel according to Mark, some time after Paul's death. From a few lines in the letter to the Corinthians we have the setting of the scene of the last supper... and possibly the germ of the Passion narrative. No Paul didn't invent it.. it was passed on to him. But he got it from those who told the stories that would ultimately become the Gospels. I think the hard part with Paul is the way that our pericopes stretch out without context. (The grievous way in which the first letter to the Corinthians is stretched out over three years.)

I used to make the same complaints as your interlocutor. Now my complaint is that people use Paul as their source of proof texting for the rightbess of their theological positions.