I don't recognise this 'workrate' Yaya everyone is going on about.
I remember a player who jogged about & occasionally sprinted forward, then jogged back, no matter how desperate the situation. A player who, if given a marking job, just basically ignored it. Never tracked opposing runners into our penalty area no matter how importantit was & regularly left his man at set pieces.
I also recall a player who is one of the best, on the ball, we have ever had.
This hard working box to box Yaya has never existed. He is a great footballer, end of.
The difference between Yaya when we signed him & Yaya now, is a yard of pace. He's not as quick as he was. Neither is Silva & Yaya is still two yards quicker than him.
If Pep wants to use him, he'll be fine, as a footballer. If he doesn't want to use him, he won't play.
If he wants him to make 60 yard defensive runs, he won't do it very much. Neither will Silva. They will both do it about the same.
Silva presses and harries far more than Yaya and has more tactical intelligence (or willingness to adhere to the tactics).