You know, the more I think about his assertion, the less I think it’s true – in fact, I think Jesus is explicitly saying exactly the opposite, in direct speech, as found in the Bible!
Look at Matthew 16:19. Speaking solely to Peter, Jesus says, “I will give you the keys to the kingdom of heaven. Whatever you bind on earth shall be bound in heaven; and whatever you loose on earth shall be loosed in heaven.”
In the first sentence, Jesus is giving Peter authority; in the context of the adminstration of His Church, Jesus grants leadership to Peter. In the second sentence, Jesus explains what that effect that authority has: what the Church binds in its declarations on earth, Jesus will hold bound from heaven; what she looses, Jesus will hold loosed.
The practical upshot of this is that the Church – led by Peter – will administer Jesus’ Church. In the context of that administration, she will naturally provide interpretations of what Jesus meant and what the content of the Church’s faith will be. Jesus promises that He will adopt these interpretations – no ifs, ands, or buts.
Now, I ask you: if Jesus says “I hold you to X, Y, and Z, and I loose you from A, B, and C,” aren’t we – as Christians – obliged to listen to Him? Aren’t we called to follow what He says to follow and reject what He says to reject? So then, if the Church’s declarations have Jesus’ thumbs-up, aren’t we obliged to follow them?
I would say that Jesus’ proxy in Mt 16:19 is precisely what your brother is rejecting – and that’s surprising, since we’re not talking apostolic teaching here, but the red-letter words of Jesus Himself in Scripture! I think I might point your brother to that verse in Scripture and ask him what this verse could possibly mean, other than that the Church has Jesus’ authority here on earth with respect to declaration of doctrine and administration…?