In what way does it mean we "lose the huge initial impact of Doyle", 1950? On the contrary, his aptitude for the inverted FB role enhances his impact in possession, not only by utilising his passing skills in a more advanced position, but also by freeing two of the midfield trio to get forward in support of the front line. Received opinion is that that is why we wanted him, and his playing that role is why Man City agreed to let us have him.
So far this season, playing at LB, Doyle has 1 goal (open play) and 4 assists; playing at CB, he has just 1 assist. That suggests to me that his impact has been much as Thorup and Knapper hoped it would be.