Have you realized perhaps an easier explanation is that Peter, who spent about 40 days with the post resurrected Christ, whom taught them everything pertaining the Kingdom of God (Acts 1:3), understood Matt 28:19-20 very differently from how you would understand it in the English language?
As I have stated to 7seas elsewhere in this thread:
One point I would like to raise where the Bible translates the Greek into this term "all nations". May I suggest that the meaning is not exactly the same when we understood it in English.
Let me give you an example from Luke 2:1 KJV
And it came to pass in those days, that there went out a decree from Caesar Augustus, that all the world should be taxed.
Young's version goes
And it came to pass in those days, there went forth a decree from Caesar Augustus, that all the world be enrolled
I am presenting a view that when we read "all the nations" in the Matthew version of the GC, it may not mean exactly what we think it means in the English. It could point towards "all the known Jews in the Roman Empire".
Of course, you could be correct, I am not denying that possibility. I am saying there could be another possible explanation, that every Jew at that time have a different idea from you about what preaching to "all nations" really meant.
You still seem to be ignoring Peter himself saying he was sent to gentiles, this in iteself disproves that he was not sent to gentiles:
Acts 15:6-7, “So the apostles and the elders met to consider this statement. After a lengthy debate, Peter stood up and said to them, “Brothers,
you know that in the early days God chose me to be the one among you through whom the Gentiles would hear the message of the gospel and believe."
And what you are saying makes no logical sense because Mat 28:19 uses a differnt greek word than Luke 2:1
Matthew 28:19-20, " 19 Go therefore and make disciples of all
nations (1484. ethnos), baptizing them in the name of the Father and of the Son and of the Holy Spirit, 20 teaching them to observe all that I have commanded you. And behold, I am with you always, to the end of the age.”
1484. ethnos
ethnos: a race, a nation, pl. the nations (as distinct from Isr.)
Original Word: ἔθνος, ους, τό
Part of Speech: Noun, Neuter
Transliteration: ethnos
Phonetic Spelling: (eth'-nos)
Definition: a race, a nation, the nations (as distinct from Israel)
Usage: a race, people, nation; the nations, heathen world, Gentiles.
You will see word #G
1484. ethnos does not appear anywhere in Luke 2:1
Luke 2: 1 And it came to be in those days that a decree went out from Caesar Augustus for
all the world to be registered.
3956 [e] πᾶσαν
pasan all Adj-AFS
3588 [e] τὴν
tēn the Art-AFS
3625 [e] οἰκουμένην.
oikoumenēn world. N-AFS
Mat 28 literally says "gentiles" that is non-Israelites. So for anyone to claim Peter and the 12 were not sent to gentiles is 100% directly in oppisition to the words of Jesus.