What it mainly boils down to is that the Holy Spirit led the Church to define the canon in the way that it is in now, so regardless of what could have been, we can trust that the Church was led by the Holy Spirit to define the canon. The definition of the canon is just as inspired as the Bible itself.
That being said, there is great edification and value in the letter of Barnabas and the Shepherd of Hermas. There is a lot of Apostolic DNA running through those writings. In fact I believe the traditional understanding that St. Barnabas is the author and St. Hermas.