There are many problems with our midfield but IMO it can all be summed up as "pedestrian".
We take too long to win the ball back or to press and we take too long to move it about and create chances.
Someone like Fabregas brings that energy and speed to the midfield. I think somebody like him would approve us across the board. He can do a bit of everything, a genuine box to box player IMO.
Somebody like Kroos, although he would improve us loads, is less suited I think. As good as he is he also plays at a relatively slow speed. However, it seems that may be what LvG prefers.