Michael Grant is not the only person who considers the martyrdom of Stephen to be a literary device by the author of Acts. The respected theologian, Raymond E. Brown says in An Introduction to the New Testament, page 296, that the scene involving Stephen’s trial and death is significant because the death of Stephen in Acts matches so closely the death of Jesus in Luke's Gospel. On page 320, Brown says we can never verify the existence and martyrdom of Stephen. On page 423, Brown casts further doubt on the entire story of Paul in Acts of the Apostles, by pointing out that Paul is described in Acts 7:58 as a young man at the stoning of Stephen and in Philemon 9 as an "old man” (Which usually implied age 50 to 60).
Acts 22:3 does say that Paul was educated at the feet of the great rabbi Gamaliel, which would certainly mean that he had been in Jerusalem some time before the death of Stephen, no doubt in the late 20s. To this, Brown says (ibid, 425-6) the claim that Paul was brought up in Jerusalem and educated by Gamaliel probably needs qualification. Paul's letters do not suggest that Paul had seen Jesus during the public ministry or at the crucifixion, and so implicitly cast doubt on Paul's continuous presence in Jerusalem in the years 26-30/33. In his epistles, Paul wrote many allusions to the Old Testament, but only ever referred to the Septuagint, even when a Jew accustomed to the Hebrew scriptures would have considered those citations erroneous. Since Paul shows no evidence of knowing the Hebrew scriptures, there must be considerable doubt whether he was really educated in Jerusalem, by Gamaliel or any other rabbi. Paul is most unlikely to have been in Jerusalem during the lifetime of Jesus.
Paul does not say in Galatians that he had never been in Jerusalem before his conversion, so this is possible, but unstated. He only says that when God revealed himself in Paul, Paul spoke to no one, but went immediately to Arabia and not to Jerusalem:
Galatians 1:15-17: But when it pleased God, who separated me from my mother's womb, and called me by his grace, To reveal his Son in me, that I might preach him among the heathen; immediately I conferred not with flesh and blood: Neither went I up to Jerusalem to them which were apostles before me; but I went into Arabia, and returned again unto Damascus.
Following his conversion, Paul says he first went to Jerusalem after his visit to Petrea (Arabia) and then three years in Damascus. We do not know the exact year of the first post-conversion visit to Jerusalem, but King Aretas was given control of Damascus by Emperor Caligula about 37 CE, and Aretas died in 40 CE, so the escape from Damascus was during this period. The first confirmed visit by Paul to Jerusalem would therefore be in the late 30s CE.
Uta Ranke-Heinemann, in Putting Away Childish Things, page 171, cites the German theologian Hans Joachim Schoeps, to say that Acts follows a clear didactic line and for this reason energetically cultivates the creation of legends and reshapes persons and events according to its own standards. In effect, supporting the contention that the story of Stephen's martyrdom was a literary device to introduce the callow youth, Saul, as a foil for the great Christian missionary he would become.