Did Reb Shimon Bar Yochai Author The Zohar ?

Did Rashbi author the Zohar? The Rema writes he heard, that Rashbi authored the Zohar. There is a Machlokes תנאים if גיד הנשה is מותר or אסור  בהנאה (benefit)  Reb Yehuda holds that it is מותר and R. Shimon* holds it is אסור בהנאה.  The Bais Yosef (Y.D. 65) writes:  "It is best to refrain from having הנאה  from the גיד הנשה because The Zohar  פרשת וישלח writes that גיד הנשה is אסור בהנאה."  The Rema in Darkei Moshe writes that he heard "(שמעתי) that the author of the Zohar was R. Shimon (Bar Yochai)  the same one who is mentioned in the Talmud. The Rema asks, If this is true, then why should we care that the Zohar holds that it is אסור בהנאה. We have a rule whenever there is a Machlokes between Reb Shimon and R. Yehuda the Halacha is like R. Yehuda." I find it puzzling, if we assume the Bais Yosef also held that the Zohar was written by R. Shimon B.Y.  How does he claim that we should follow R.Shimon's  ruling in the Mishna because R. Shimon in Zohar also agrees. It's like saying that he is right because he himself said so. Perhaps we can explain, the Bais Yosef means to say, to be מחמיר because even על פי קבלה (Zohar) it is אסור בהנאה. According to this, we can answer the Rema's Kushya. True Halachacially it should be Muter because we always Pasken like R. Yehuda against R. Shimon. However, according to **Kabbala (Zohar), it is אסור בהנאה like R. Shimon.  אמבצי   *סתם ר' שמעון הוא רשב"י ** עיין מ"ב ס' כ"ה ס"ק מ"ב בשם הכנה"ג