So there are no stats to show how many chances created by Silva and Mata are wasted. Mata takes set pieces too at which Chelsea are good, chances are created from set pieces too?Drogba and Torres have scored a combined 16% of Chelsea's total PL goals, so clearly that argument does hold. ****, include Sturridge and that's a combined 32% of their total goals. Compare that to City where Aguero has 25% of their goals by himself, United where Rooney has 28% of all their goals, Arsenal where RVP has 41% of their goals. One of the main strikers from the big teams almost contribute the same amount of goals as 3 of Chelsea's together, so they blatantly don't have as good strikers.
18% of Chelsea's goals have come from defenders, implying that they score a lot from set pieces or from defenders being in positions to score easily converted chances, since you don't expect defenders to score, or be in the positions, to score from more difficult attacking plays. This would imply that a large amount of these goals come from clear cut chances, accounting for these goals in your stats gives a new conversion rate of 33%, for the rest of the team. Not so good.
Statistics are fun
So indeed your second para proves it. Mata takes set piece so high chance creation rate?
Edit: How do you prove that forwards wasted the chances created by Mata with those stats? For all we know all the Mata's goal scoring chances fell to midfielders and defenders?