Standards are obviously low for Mata. That was the sort of performance that 21 year old Sterling gets the 'overrated' comments for.
He's good at certain technical elements, but lacking in others. And, unfortunately for him, those areas where he lacks prevent him from being a top player who can influence games, especially when there isn't a lot of space.
Influencing games when there isn't a lot of space is what top players do. He doesn't have the skill set - thus it's always the fault of someone else, apparently.
Someone mentioned him needing a system that shields him. What the heck are his team-mates going to do? Create a human shield every time he gets the ball, and bundle through?
Put Silva in this team (yes, even this team) and his superiority in receiving the ball, turning his man, dribbling past people, making the ball stick... would become apparent. He's the type you build around.
Mata will probably leave, and yes, he'll look better. But it'll be to a lesser club, where they play on the counter every week, and they're just so thankful to have him, so they let him do what he wants every game, and ignore his flaws.
He'll look good in the same way Bolasie looks good at Palace but wouldn't at a team who actually look to dominate possession (which requires more skill). Palace would suit Mata, actually. And they're closer to his level than the top teams/clubs in Europe.
Some even call him world class for his two good seasons at a poor Chelsea (where Ivanovic, Drogba, Cahill and Terry made it hard not to rack up the assists from set-plays). Yet they wouldn't call Sturridge world class for his 1.5 years of goals galore.