Lower Westelrey Rodgers was hired by people who should have known what he was, a manager who wants to play passing football. If you hire the wrong person, who's fault is it?
Rodgers attempted to impose a formation/style of play on a squad that wasn't up to the job.
Brian stepped up to the mark. Reverted to a 4-4-2 formation and the rest is history.
This is a little revisionist. McDermott only used 4-4-2 when he was protecting Sigurdsson - and then when he had to sell Sigurdsson. Rodgers also used it quite a bit when he was here - this was actually one of the big complaints people had, he was sticking Gylfi out on the left instead of using a formation that suited him.
The big differences he made were recalling Kebe, Long, Mills, and Gunnarsson from the wilderness. We still mostly played 4-2-3-1, which was also the formation Rodgers had mostly settled on.