So to get to the gist of it, a bishop is secure in a position of almost absolute power. And you know the expression, ‘power corrupts and absolute power corrupts absolutely.’
Jesus promised that the gates of hell would not prevail against His Church ... and, after 2000 years, the Church is still vital and thriving, despite bad priests, bishops, cardinals and even some bad popes.
Your statement fails when it comes to the good bishops and we all know who they are. It's all relative.