I think that we played 3-5-2 and lost 2-0 to Chievo IS De Boer's fault. That was his choice. The starting XI was his choice.
For preseason, I blame management.
For the personnel at De Boer's disposal, I blame management.
For Orlando Trustfull as Assistant Manager, I blame DeBoer. (so again, the 3-5-2 and 2-0 result is his fault)
For Mancini's lacklustre spell, I give a lot of the blame to management, a little to Mazzari, and slightly more to Mancini himself.
The club has been without a rudder for 5 or 6 years! My view is that Mancini got entirely too much of the blame for the shitshow that was Inter, not that he was entirely without blame. And we still haven't sorted out our personnel problems.
As for Icardi's shortcomings, I blame Icardi. He had the chance if he wanted to become a better, more well-rounded striker, who can hold up play, link up with team mates, press when the team loses the ball...
Regarding coaching, I know that if you have 22 players you may need up to 22 coaching styles, and this is going to come as a shock to some, but COMMUNICATION IS CRUCIAL.