Cases brought to court and overturned are a rare exception if the vast majority of cases aren't brought to court. You are measuring two related variables the cases that are brought to court AND overturned ... and that is not 50%. Any case which is either not overturned or not brought to court in the first place go against what your claiming.

Cases that have not got a realistic chance of being overturned should be going to court.

Furthermore that is not the only reason that appeals should happen. Appeals can happen for a variety of reasons including that further information is brought to light that was not there in the original decision making process. If the original decision maker is clear, consistent and reasonable about why they've reached their decision then that can help rule out flippant appeals and concentrate appeals only on those with a substantive issue which are more likely to succeed.