I don't think Sneijder can be blamed for all our failures this year. I know it may seem weird that when Sneijder plays we've actually done worse than when he does play, but if you watch the games you can understand why. When he is not in the line up the team plays like a more collective unit. They know that no one in particular is gonna spark the offense and so they work together in attack. The opposing teams defense also does not have any one particular player to mark, and so they don't pay any special attention to any one player.
When Sneijder plays inter are always looking to play through him. When he has the ball, very rarely do you see any positive off the ball movement from the other inter players. At times he looks like he is the only one trying. Also, the opposing team realize this and immediately double and triple team him, as they figure if they can neutralize Sneijder, they can neutralize our attack.
With another offensive talent, even someone that plays deeper in the midfield, it would give Sneijder more space. We saw this when inter won the treble and we see it every time he plays with Holland. He is a talented player, but unfortunately the players he is playing with are not all on his level. I think with Sneijder playing with players like Alvarez, Coutinho, Guarin, and a player like Banega, we will see a more effective Sneijder.