NONSENSE.

Jesus is the Gospel. Sent by the Father.

The other 11 Apostles taught for 3+ years BEFORE Paul.

What were THEY teaching?

Gospel of salvation was given to Paul?

Point #1

Salvation actually comes from God. The Father...OUR Father...SENT His Son Jesus to us.

And EVERYTHING Jesus said was FROM the Father.

See this.

John 12

49 For I have not spoken of myself; but he Father which sent me, he gave me a commandment, what I should say, and what I should speak.

50 And I know that his commandment is life everlasting: whatsoever I speak therefore, even as the Father said unto me, so I speak.

Point #2

Our Father...Abba...Jehovah...Yahweh...had NUMEROUS prophets telling the people to REPENT in the Old Testament.

AND He told Isaiah to tell the people...

Isaiah 1:18 Come now, and let us reason together, saith the LORD : though your sins be as scarlet, they shall be as white as snow; though they be red like crimson, they shall be as wool.

BOTH John the Baptist and Jesus preached repentance.

Matthew 3:2 and saying, "Repent, for the kingdom of heaven is at hand!"

Matthew 4:17 (KJV) From that time Jesus began to preach, and to say, Repent: for the kingdom of heaven is at hand.

Point #3

That said, here's Jesus AGAIN...about both repenting...AND "believe the gospel".

Mark 1:15 And saying*, The time is fulfilled, and the kingdom of God is at hand: repent ye, and believe* the gospel.

Matthew mentioning the "preaching of the Gospel".

Matthew 4:23 And Jesus went about all Galilee, teaching in their synagogues, and preaching the gospel of the kingdom, and healing all manner of sickness and all manner of disease among the people.

Point #4

The 11 original Apostles and Matthias were preaching the gospel of salvation for at LEAST 3 years BEFORE Paul, as he spent 3 years in the desert.

By YOUR analogy, their preaching meant nothing.

Point #5 - LAST but MOST Important

THESE are the MOST significant words Jesus said about Salvation.

John 3:16 (KJV) For God so loved the world, that he gave his only begotten Son, that whosoever believeth in him should not perish, but have everlasting life.

Paul was just another Apostle sent out by Jesus. No better....no worse. His letters to the various churches dealt with probems in those churches, and documented his efforts to resolve them as much if not more than giving additional instruction.

He was sent NORTH...NOT to the places the OTHER Apostles had already been to.