The FW36 has been pretty quick all year, of course having the Mercedes powerunit has been a massive benefit to them but you cannot underestimate the job they've done aerodynamically. The FW36 is an efficient car, not strewn with aero components that force the airflow. This methodology does put more of an emphasis on mechanical grip and is likely the reason they struggled with tyre wear early on. Once they had a good handle on that they made much larger strides to the front of the pack.
The use of the Y100 winglet / monkey seat is also eradicated for Monza as it's primary use is to connect the airflow structures, making for a more efficient rear wing at lower speed (aiding in attachment). Without the angle of attack the rear wing doesn't need assistance from a Y100 winglet in order to operate at its optimum.