Oh there is certainly enough blame to be shared around!
But you'd like to hope that a manager worth the salary that Koeman is being paid would show some improvement, however marginal, in either tactics or performances over the few months he has been here, especially as he was clearly brought in to be a quick fix rather than someone who developed the youth players.
He shouldn't have to replace the entire squad before we can see some of his ideas bearing fruit on the pitch - plenty of managers have improved defensive results for instance with just coaching and yet we still seem very vulnerable to set pieces and crosses.
Playing 3 defensive midfielders away to Watford and still losing by 3 goals might be all the players fault in his first few games but by game 15?