"accurate in so much fine detail" - and inaccurate in thousands of other cases.
Thousands?
'Mark's' geography is all wrong, Jesus' ideas about how a farmer goes to sow valuable seed is ludicrous, and the 'fine detail' of the Resurrection accounts contradict each other in every instance. Matthew describes the 'miracle' of the angel coming down in front of the women and rolling away the stone, and causing the guards to faint in the process, whereas Mark doesn't mention this at all. The women (different quantity) just see the stone rolled away, and a young man sitting there. So who witnessed the miracle of the descending angel, and why did Mark not describe his dazzling, supernatural appearance (particularly if he was borrowing his material from Mattthew, which is your other hobby-horse)?
John Mark's mother lived in Jerusalem, and the disciples used her house to meet in. See the account in Acts where Peter escapes from prison and goes there. It's possible therefore that John Mark had limited knowledge of Galilee, where many of the events took place. In the account attributed to him, we are given details such as the name Bartimaeus and the two sons of Simon of Cyrene (one of whom, Rufus, may have been known to the church in Rome, for whom Mark is said to have written. Paul also refers to a man called Rufus in Romans 16); both occur during Jesus' final weeks in the region in and around Jerusalem, and both are absent from Matthew and Luke. If the author of Mark was John Mark, that he was from Jerusalem would explain why he could give details that would have been known in the church there. However, we would expect that details relating to regions he did not know might be inaccurate.
The parable of the sower isn't meant to be a farming lesson. The word is actually "one sowing, not farmer.
Regarding Matthew's resurrection account: where do angels come from, and who else would have rolled away the stone? The women only needed to see him sitting on the stone for it to be inferred that he came down from heaven, rolled the stone away and sat on it; so there is no contradiction. Mark's description of the stone is less natural than Matthew's, and is a reference back to it. Mark's 'young man dressed in white' is a description similar to the description of the angels in Acts 1; the white clothing, as well as sitting posture and his words to the women, are in agreement with Matthew. Remember that Mark conflated Matthew and Luke and at times hints that he has knowledge of John's gospel.