Spetuagint Greek is not the same as New Testament Greek.
This is true in so much as the Septuagint is often more Hebraic than the NT, but it is also true that Septuagint Greek is not the same as Septuagint Greek. The translations of the LXX texts occurred over a period of centuries, quite possibly spanning the time from three centuries before Christ to perhaps a century
after (in Ecclesiastes). It is not a single work, but a compilation, and the language is not consistent throughout, with parts of it (e.g., the Torah translations) being quite Hebraic and parts (e.g., the Maccabees) more truly Greek. This is what makes Edwin Hatchās label āBiblical Greekā so apt.
The details of the relationship between Aramaic and Hebrew I cannot comment upon, since I read neither.
Unfortunately I donāt remember the source, but I remember reading that KoinĆ© Greek did not totally replace it (because it is not Semitic?), and that Aramaic did not go into decline until Classical Arabic replaced it with the rise of Islam.
Īοινη never replaced Aramaic because they served different functions: Aramaic was the local language, Īοινη the language of communication across distance. As time passed, Īοινη developed into Byzantine Greek.
As for Mt 16:8 and PRotestant deconstruction: I have had to point out that apparently the only dictionary that defines āpetrosā as a pebble or little rock is Vineās which has its own bias. Of course, "Kephaā " in Aramaic is masculine. Protestants hang on Vineās and try to claim that the Catholic Church only claims Jesus and the Israelites spoke Aramaic to justify the position of Peter. However, I have a modern (19th-century) Greek-English dictionary that only has āPetrosā with a capital P and defined as a given name.
Some Protestants do that, I know: I, too, have met them. They really ought to reread such passages as Mark 5:41 and 7:34, in which the Gospel writer says that Jesus was speaking in Aramaic.
That said, I have run into non-Greek-reading Catholic apologists who so earnestly want to assert that Mt 16:18 refers ājust to Peter - only to Peter - to no one but Peter - no, Iām not listening - my fingers are in my earsā that they miss what
else the text is saying there. The passage is a neat play on words in Greek which does not translate well into English, but Lampeās
Patristic Greek Lexicon explains the various ways in which the Greek Fathers, reading in their native tongue, appreciated the depth what was written there.
BTW, ΠεĻĻĪæĻ, a common noun which became a personal name after the original disciple, was occasionally feminine (q.v.
Anthologia Palatina 7.274, 479).