Silvestre came in 2012. He was not Mazzarri's.
You really think Mazzarri bought all those players? He was the Napoli coach with Cavani, Lavezzi, Hamsik. Then he came to Inter and asked for Belfodil, Vidic, Hernanes, Dodo? I'm sorry but my logic refuses to accept this idea. Imo, transfers are usually done by the club with the reference to the requirement of the coach. Mazzarri was probably not a whiny bitch and settled with whatever he was given but to believe he was the one who spent those money? We know who Moratti post-treble too well tbh. Also, do remember, Mazzarri came under Moratti who didn't really support the coach. In November, which is about 3 months after he began his journey, Thohir came. That was the only full season he got.
Again, had Mazzarri got the support like Mancini was supported by Thohir, then we can compare them. Actually, Mancini should have done much better as he got many of his wishes.