At the AAIE Conference Grape Roundtable I show slides about distinguishing sulfur damage from thrips damage in table grapes. I have more information in two articles on my page:
Sulfur causes "false thrips scars" in grapes.
Stamen-Anther Scarring in Grapes; Not Caused by Thrips.
The articles also give evidence that sulfur does cause damage.
In my thirty years of monitoring table grapes, I have seen far more sulfur damage than thrips damage.
A lot of thripicide sprays are unnecessary, and also disrupt biocontrol of other pests such as mealybugs.