SUPERNATURAL or MIRACULOUS powers are the hangover of the earlier age when events of Ramayan were not understandable, because of the lack of information with the general public, and maybe by the religious leaders of that time. So to explain certain events INTERPRETATION and INTERPOLATION were used. Some have found mention in the Valmiki's Ramayan too. Remember Treta Yug existed at least 5,00,000 years earlier.
Remember that we are living in an information age and once we believe that there were flying machines too, at that time, we have to understand history of that period with the sophistication it deserves. We cannot believe that the sophisticated Lankan forces were vanquished by the crude stone throwing Vaanars simply because of supernatural powers that Shri Ram possessed. NO SUCH THING HAPPENED. Vaanars had received military training during last 12 to 13 years and they also had a better and more able leader in Shri Ram, which ensured their victory.