You are incorrect. For the majority in AD150 could not read at all therefore they had to be taught to either read for themselves or take someone's word as to the veracity of the message. In addition, folks in AD150 had the added benefit of hearing from second generation disciples of the original twelve. Hence, your refutation falls apart at the outset.
Furthermore; in AD150 though the common language of the empire was Greek, the disciples had been scattered hither and yon into countries in which the commoner did NOT speak Greek and depended on translations , the Old Latin being one of many.
Therefore; they had to be TAUGHT the meanings of words just as we do today. My logic holds true in spite of your weak attempt to refute it. You will have a tough sell convincing any competent teacher that you can present ANY document of the caliber of Scripture to their students which they will NOT have to look up the meaning of some of the words. As a matter of fact, I challenge you to produce any version, valid or no, which is totally understandable by ALL who read it.
Nehemiah 8:8 So they read in the book in the law of God distinctly, and gave the sense, and caused them to understand the reading.
Acts 8:30-31 And Philip ran thither to him, and heard him read the prophet Esaias, and said, Understandest thou what thou readest? And he said, How can I, except some man should guide me? And he desired Philip that he would come up and sit with him.
Even God's word itself shoots your assertion in the foot. It is clear that God's word WILL NOT be understood by all who read it or hear it.
Though I agree that Scripture should be understandable (humanly speaking) to any who can read, I can testify to you that it will NOT be, in spite of the BEST efforts of supposed 'godly men'.
This concept that God's word should be so simple that a child can understand it is a perversion of the truth that the GOSPEL IS that simple. For although the GOSPEL is simple enough for a child, even Peter has declared that there are some things (words included) which are hard to understand, hence the NEED for a teacher. Hence the COMMAND of Christ that WE should go and TEACH!
It is just too simple minded to assume that we can dumb down God's word to the level of a preschooleror even a grade school kid. For even the CONCEPTS such as propitiation are struggled with by greater scholars than you or I. Did you know what propitiation was without looking it up or being taught? I didn't think so.