Completely agree with this. I have always been of the opinion players are by far the most important element of potential league position, but a manager has the ability to push the players to the edge of their potential.
To put it rather simply, a given set of players has a range of potential finishing positions. A good manager pushes the players to the top of that range, while a poor manager pushes the squad to the bottom of the range.
I think this squad has a range of about 14-20. Under that supposition, Lambert is doing a average to poor job. That being said, I think it would take a very good managerial performance to even get this set of players a lower mid-table finish.