I've never understood this opinion on the "prophesy", he did bring balance to the force. Before him there were many Jedi and few Sith, afterwards the force user numbers were balanced. He would have been much more powerful if he had started training at a younger age, but then he would have been less likely to have turned to the dark side as he wouldn't have had the emotional attachments he formed as a child. He only had something like 12 years of training before being given the rank of master, rather than training for 20 years before earning the knight rank as was the norm.