A fraud - to me is a description of character, something permanent. Suggesting he never should haven been manager in the first place. I think that’s disrespectful and wrong. He’s won the league FFS.
clueless and having lost the plot - to me those are temporary/state of mind. Not being able to solve the current problem. It’s not hard to see where that criticism comes from.
I think only the first is a permanent stain on his character, yeah I’d call that vitriolic. The other two are disrespectful, but I wouldn’t say over the top, let alone vitriolic.