EE has a career OPS just a shade under .800 with this being his 3rd full season at the MLB level all before he turns 25. He is just slumping right now, he will be fine. Brantly and Marty need a whipping boy and its EE's turn since they seem to have laid off Dunn for whatever reason.
It isn't widely known that he can't handle an outside pitch, people throw it out there because like a lot of young players he will chase breaking balls on the outside half.
The only person I have heard say anything about EE and the outside pitch is Chris Welsh and if you want to convert his pearls of wisdom into something being "widely known around MLB" then nothing anyone else can say is going to have an effect.
Just remember that if Marty/Welsh/Grande/Brantly were doing football you'd be hearing a lot about SEC speed and how slow
OSU was. Just because they are calling the games doesn't make what they say neccessarily so.