Mata is the epitome of a no. 10. Creative, technically very strong and operates in the space between the opponent's defence and midfield. If that's not a no. 10, what is?
I see Silva as a number 10. And I think he's very different to Mata.
Mata's more of an instinctive player than a dictator of play. Looks best when the game is more stretched and he has space to use and can time his runs late into the box.
Whereas a number 10 excels with holding the ball (and waiting for that pass) even when penned in the final third under tight marking.
A number 10 often finds themselves isolated and needs to hold the ball without the space to build up speed. At in these circumstances when I think Mata goes missing. A bit might be due to a lack of patience in his play.
Mata at his best, is all about great control, passing it short and moving up the pitch for the return. He can obviously thread a final pass - very well, but so can Kagawa, and I see him as a second striker too. And playing those passes doesn't ake them number 10s.
His close control is brilliant, and he has it in him to play it about well, but he doesn't dictate the game or leave his mark on the game like a proper number 10 for me. He tries (as it's expected of him), but I doesn't seem natural to him, and I actually think that takes from his game, which is more geared towards being direct and closer to goal being instinctive.
It's hard to explain really, but I don't see him as someone to build a successful side around. And I definitely wouldn't give him the role of number 10, let alone midfield. I also don't think he shields/protects the ball well enough when starting from stationary, which means he has to release quickly - which isn't ideal for a number 10. The ball doesn't stick to him when he's tightly marked and slowed down.
It's an unpopular opinion, and I'll probably be replied to by a Chelsea fan telling me I'm completely wrong, but that's just how I see it.
He's never come across as a proper number 10 to me.