This man, then, was glorified by many as if he were a god; and he taught that it was himself who appeared among the Jews as the Son, but descended in Samaria as the Father while he came to other nations in the character of the Holy Spirit.
I would have expected, from the first time I read this passage, that Irenaeus would have said rather:
This man, then, was glorified by many as if he were a god; and he taught that it was himself who appeared among the Jews as the Son, but descended in Samaria as the Father while he came to other nations in the character of Paul the Apostle.
So, if Irenaeus is correct that the Magus did that claim, then the same words of the Magus would be evidence that there was not a colossal apostle called "Paul" working among the nations, but only the Holy Spirit, who would have inspired a lot of little Pauls in the world.
So Paul could be merely an invented icon for the anonymous figure of the apostles inspired by the holy spirit. The name itself, 'Paul', alludes to the fact that when one is inspired by the Holy Spirit, his personality doesn't matter more, he becomes little so that a distinct being, the Holy Spirit, can talk completely in his place.