I don't know. He's decent, but it's not just our system, he's just not capable of playing at this level I think, it's too fast and too physical. Last year people blamed Allardyce for the fact he didn't look great, this year it's Silva. It seems far more likely to me that he just isn't good enough.I totally agree that we overpaid for him as you said and his contract, while nowhere near as bad as some of them, is a definitely a stumbling block.
My point is that, in my humble opinion, he is actually a decent striker who now unfortunately doesn't suit our current needs and this negates his ability.
For me, he showed last season that he's much better than all the players that I mentioned and 'could' offer something in the future; they certainly will not.
To be fair, all of the players you've mentioned fall into a similar bracket. For all people like to make out that players who don't do well for us are League 2 standard, most of them are decent in their own right but just not up to scratch for a team in the top half of the PL. Just look at Bolasie now, he's on track to absolutely smash his best ever goalscoring season despite only joining Anderlecht at the end of January, because the Belgian league, like the Turkish one, is not comparable to the PL. I'm sure Sandro would find his scoring boots if he went and played in Turkey too.