I don't understand Rav Shimon's sheeta - it seems that he doesn't accept the concept of muktzah. Isn't muktzah a major gezerah d'Rabbanan dating backat least to Shlomo Hamelech's time or earlier? How can he not accept it? Could someone not accept the 2nd day of Yom Tov (outside Israel) or decide that he can carry a shofar or lulav/etrog on Shabbos because he doesn't accept the gezerah?
Rebbi Shimon certainly accepts the concept of Muktzah, as we find on Daf 45a. However, he maintains that the Gezeirah of Muktzah is much more limited in scope than Rebbi Yehudah holds. Indeed, the Halachah follows Rebbi Shimon on Shabbos, and the laws of Muktzah on Shabbos that we follow today are all basically in accordance with the view of Rebbi Shimon.