Yoda was competent but he never did defeat a major character. He tried to be the rock of the JEDI in their most tumultuous time. Don't blame Yoda for everyone elses mistakes, Yoda may have seemed like he made many mistakes, but in the end he really made none, when you look at it from the point of view of the Force trying to regain balance, and suffering from imbalance. The Dark Side covers all, I thought it was funny how Luke treated him. It was like "yeah, whatever little man" over half the time.