Those European authorities were either complicit, or unfit to oversee European finance. Therefore their oversight of the proposed unified European banking union might be unreliable. Any shortcomings would affect the whole unified European banking system. Individual national banking oversight is safer, because oversight risk is spread about, instead of concentrated.
"ECB tells court releasing Greek swap files would inflame market". I acknowledge JSMineset for bringing this article to my attention.
"Dangerous EU banking union proposed".
"How Goldman Sachs helped falsify Greece's national accounts".