At this point last year, Stramaccioni and everyone else already knew that he'll be replaced due to poor results. And Stramaccioni had 50 points after 31 rounds. Mazzarri has 49 points.
I'm not sure how big his influence was in the transfer market, but in his time Inter got rid of Cassano and spent a total of 45m eur on new players. And they only had serie A, while Stramaccioni's Inter had 12 matches in Europe last year.
Frankly, it's close to impossible to do much better with the players he has. They are average or below average players that have to cope with big expectations, only because they play for Inter. But so was the case with the rookie they had on the bench last year, and that rookie got the sack for less.