We must also note that in every instance in the scripture where traditions are referenced, they are referenced in the past tense, as something already received and learned, not as something that would continue to evolve over time with additions from fallible men, but as something shown by the example of the apostles and followed until the scriptures as we now know them could be completed.
Again, he’s assuming his conclusion. The Church received several promises from Christ, including that the gates of hell shall never prevail against His Church, that whatever those in authority in His Church bound on earth would be bound in heaven, and that the Holy Spirit would lead His Church to all the truth.
That means that Christ promised these “fallible men” with His heavenly power and grace to teach infallibly. The same “fallible men” which he thinks “added” or “evolved” revealed truth against God are no different than the “fallible men” who penned the books which comprise the BIble and which he, rightfully, asserts are infallible.
It simply doesn’t follow that if God empowered the “fallable men” known as the Apostles to write infallibly that God could not continue to empower their succesors to do the same when expounding or explaining the traditions they had received from the Apostles.
He seems to rather be conflating the terms “added” or “evolved” with the term “developments”. And are those things which he claims are additions are really not just developments that still maintain the essence of what was already revealed?
I fully understand the lack of literacy and access to written works in the first century, but I also turn to passages like 1 Corinthians 14 to see that in the first century church individuals had spiritual gifts that allowed them to know the will of God in the interim. In the preceding chapter, Paul even went so far as to prophecy that when the scriptures had been completed, spiritual gifts would cease among the saints.
The claim here is rather vague. If he is referring to 13:8, he’s ripping the verse out of context as a pretext for his assumption of sola scriptura. Paul in the context is talking about (agape) love and how that love is perfect and will always remain. He then is contrasting (agape) love with other spiritual gifts(because in the context he is asserting that all spiritual gifts flow from love and are grounded in love). Thus he says that when the “perfect”(the new heavens and new earth) come what is partial-“prophecies”, “tongues”, and “knowledge”-will pass away.
He sums up his thought at the end of chapter 13:
 For now we see in a mirror dimly, but then face to face. Now I know in part; then I shall understand fully, even as I have been fully understood.
 So faith, hope, love abide, these three; but the greatest of these is love.
There s simply nothing in either context which supports “sola-scriptura”. He’s just imposing his idea onto the Scriptures.