The problem with this is that you can always find a fan who'll have a negative opinion of any manager.
We could easily find negative comments on here about Sami, Oscar, Gus, Slade, etc through every manager of recent times. We need to look deeper at the evidence.
Sherwood or Rosler or anyone else could also turn out to be 'a nightmare appointment'.
We don't know how things will unfold, so best not worry about the new man being a disaster at this stage.