With Marchisio coming back, Pjanic should be a bit better. To make it even better, I think we should play Lemina as B2B more. Kherdia can't play 3 matches in a row anyway and Lemina would make up for Pjanic's physical and overall defensive weakness. He'd add more dynamism and toughness to the midfield as well.
The other part is linked to the system, I'm afraid. Pjanic needs runners who attack open spaces and move a lot. Otherwise all he'll do is some back passes.
Allegri surely has a headache when it comes to Pjanic and he has to readjust the system. We're not getting the most out of Higuain either so there's a lot of things to improve despite the fact we're winning most of our matches.