Well, NT eyewitness was one rule, which was an OT rule.
Even as they delivered them unto us, which from the beginning were eyewitnesses, and ministers of the word;
For we have not followed cunningly devised fables, when we made known unto you the power and coming of our Lord Jesus Christ, but were eyewitnesses of his majesty.
(Christ) And said unto them, Thus it is written, and thus it behoved Christ to suffer, and to rise from the dead the third day: And that repentance and remission of sins should be preached in his name among all nations, beginning at Jerusalem. And ye are witnesses of these things.
To what point? To proclaim Christ, but as they would die, they HAD to write it down that WE who were not witnesses would know with certainty, believing that we might have life in Him (Lk, Jn, Peter, Paul, etc).
Is. 30:8 Now go, write it on a tablet before them And inscribe it on a scroll, That it may serve in the time to come As a witness forever.
The rule is "thus it is written" for the OT and the NT.
What you write here has merit. The proof that Jesus of Nazareth was the messiah had to be demonstrated to fellow jews by searching the scriptures to see if Jesus fullfilled those prophecies. Christ also fulllfilled spoken prophecies not clearly found in the OT. The NT tells us he fulfilled what was spoken by the prophets when he resided in Nazareth and not in Bethlehem. Because of an oral tradition that the messiah would be called a nazarene (matt 2.23). Some attempt to connect this with judges 13.5 but in reality it is not found in the old testament.
Your post does not defend sola scripture but Apostolic Tradition. Your post is an apologetic AGAINST sola scripture, but you havent realized it.
You open your post by describing what tradition is: 'Even as they
delivered unto us, which were from the beginning eyewitnesses.'
Correct, this is the definition of tradition, " receiving and delivering" down thru generations. The origin of these traditions are from eyewitnesses (the apostles) not books nor thru individuals who believe the Holy Spirit has lead them exclusively generations after the events.
Paul said, "Now I praise you brethren that you remember me in all things and
keep the traditions, as I DELIVERED them to you." 1COR11.2
Again you point out how Christ commanded preaching to all nations and the need for witnesses. This is apostolic tradition. Here you have revealed the origins of apostolic succession. If the apostles were meant to be scribes then eyewitnesses would not be needed.
Paul says, "For
i delivered unto you first of all that which i recieved how that Christ died for our sins according to the scriptures."(1cor15.3).
Once again the terminology which defines tradition, to recieve something from a previous generation and safeguarded so one can delivered it to the next generation.
In this case it is the interpretation of OT passages concerning the passion of Christ.
In Pauls epistle to Timothy he further lays down the groundwork for apostolic succession:
"And the things which you heard from me among many witnesses the same commit to faithful men who shall be able to teach others also."(2tim2.2.) Paul further clarifies this point when he says "all scripture is given thru inspiration of God. It is not sola scripture he speaks of as is evidenced from 2 verses earlier but proper understanding of them, "But continue in the things which thou has learned
and have been assured of, knowing from whom you have learned them".2Tim3.14
Scripture speaks of baptism, yet the 'bible only crowd' cannot agree on whether to baptize in the name of each person of the trinity or in the name of Jesus. They cannot agree on whether baptism is a one time ritual or be repeated numerous times. They cannot agree on whether baptism is a vehicle for grace or just a legalistic act. They cant agree on whether it is neccesary or optional. Heck they have yet to figure out whether it should be done in triple immersion or in single immersion! (that one should be able to be figured out by reading the original koine). Within sola scripture all these points can be valid because theres no requirement for antiquity or universality or consent to establish a reliable precedent.
This goes for the rest of the sacraments, including social issues where the new crop of liberal sola scripturalists see the bible sanctioning same sex marriages.