The truth according to Bart D. Ehrman

[John V]

Yes, the traditional view is that Mark was a follower of Peter and wrote his gospel based on Peter's teachings.

Do you understand what the word "traditional" means in this context?

In this case it means that Papias (as quoted by Eusebius) said that Mark was a follower of Peter and wrote his gospel according to what peter said. Whether you consider that evidence is up to you.