At this stage of the season the starting lineup should have been:
Maignan; Kalulu, Thiaw, Tomori, Theo; Krunic, Tonali; Diaz, Bennacer, Leao; Giroud.
With the likes of Saelemakers, Adli, Vranckx and CdK getting regular playing time.
Yes, that lineup is far from perfect and there are many positions that could use an upgrade but also Pioli is at fault for failing to develop the newer players and bring them into his formation.
I think a lot of time and effort was wasted to try to force Diaz back into the AM positions when he should have developed someone like Adli or Krunic to be the direct deputy of Bennacer there. Diaz was invisible vs Inter and Spezia at AM and many times before that, by now Pioli should get the clue that Diaz works better on the right in this team.
And then you have the defence, a couple of good games for Kjaer and Calabria and suddenly they are untouchable. They played like ass and at the expense of the development of two of the most promising players we have in Kalulu and Thiaw. It's almost scandalous the way Pioli has been dealing with this.
With the formation above, you at leat have a chance vs Inter or Madrid or Man City and you can also have some options with the players coming off the bench assuming that they've been given the confidence to develop properly the way he has done with our young players the seasons before.
This is my problem with Pioli today and why I attribute the biggest part of the blame on him.