Is it possible that Stand evolutions via the arrows is due to the same arrow affecting someone multiple times?
For example, Kira got Bites The Dust after being pierced a second time by the arrow that initially caused his Stand.
Later on in part 5, the arrow under Polnareff's protection is shown to cause both his and Giorno's stands to develop to Requiem. Could it be that this arrow is the one responsible for the creation of both Silver Chariot and the Joestar Stands? And, by implanting energy directly into the stands, it creates requiems, whereas Killer Queen simply matured as the energy went to Kira rather than his Stand. I wouldn't put it past DIO to insist the most ornate arrow be used as much as possible just because it's fancier.
If this is the case, it would explain why literally nothing of note happened to Giorno after Black Sabbath hurt Gold Experience with Polpo's arrow.
Polnareff, Kakyoin and Avdol are all stated quite a few times in the story to be naturally born Stand users. You can look up their backstories here fairly easy, not to mention it was a plot point in the Alessi arc.