Also, according to John 19:39-40, Jesus’ body was wrapped in linens and 100 pounds of aloes and myrrh (roman pounds were 11.3 ounces so the weight was closer to 96 pounds). So for Jesus to untie Himself would have meant somehow manoeuvering out of the tight wrapping weighed down by all the spices.

In regards to the expert executioner, crucifixion was used as a means of public, shameful punishment for those who rebelled against Rome. It was intended to inflict maximum pain and act as a warning to others who contemplated rebellion. The province of Palestine was not a peaceful Roman occupation and there had been many who had attempted to incite a national Jewish rebellion. The fact that Jesus was crucified with at least two other criminals that day lends credence to the idea that the Roman garrison posted in Jerusalem had troop specially assigned to efficiently carrying out these executions. I think you would be hard pressed to find examples of people who survived a Roman crucifixion which attests to the expertise that these troops had in this area.

Now you may have a point that calling the disciples spineless is hyperbole, but there certainly is plenty of evidence that the disciples hardly seemed in any frame of mind to attempt the theft of the body of Jesus. Their actions leading up to that point seems to suggest they were more intent on saving their own lives rather than risking Jesus’ fate by trying to fabricate a story of His resurrection.

There is no need to exaggerate the details of the death and resurrection of Jesus. It was a horrendous treatment that He received and words could never accurately capture the pain and suffering He experienced. Also, the miracle of how He came back to life after experiencing such a death is equally beyond our ability to comprehend or explain. What is hard to swallow is the attempts that people have made to discount the reality of this historical event in order to absolve themselves of having to face the reason that Jesus allowed Himself to be put through this anguish and the life giving hope in the meaning of His resurrection: namely, that He died to pay the penalty we owe for our rebellion against God and that His resurrection gives us hope that we too will be raised to live with Him for all eternity if we accept His offer of forgiveness. No grandstanding, no exaggeration, just the truth that we all can either choose or reject.