Some things to see though. Firstly, the parts I agree on:
1. Yes - it was a disgraceful performance by Pogba. No debates about that. He was truly awful.
2. What was said behind closed doors is one thing - it's fine to blast and slam in private.
That said:
1. Can it be called "behind closed doors" when the manager then leaks it (directly or through his agent) to the Press (because Castles is very much Jose's / Mendes' man)?
2. If Jose felt this strongly, why did Pogba not only get a start, but get to play the full 90? That's not the treatment you expect towards a player that the manager feels is not only failing to pull his weight, but also lowering the performance levels of others.
In this argument, I don't think Pogba's performance level is even relevant. Frankly, we've seen equally or more abject displays from Jose's favoured sons as well - Matic and Lukaku to name just two. Jose is entitled to rant "behind closed doors", but it's telling that every time he (allegedly) has a go at Pogba, it is his favoured journos (for leaks) that come out with the quotes and words. Last time too, it was Castles who had the alleged dope and the same this time. That leads me to see it as Jose deliberately crucifying Pogba in the Press.
I've said it before and I'll say it again. No employee in any field can be held guilty for under-performing in these circumstances. As for "sand-bagging", people miss the point when it comes to sport:
1. Unlike other fields, you can't go slow and work more time when you're not at your peak. In sport, the intensity has to be at it's peak for the full game.
2. At the top, the difference between a great game and an ordinary one is tiny. The slightest dip in focus results in "horrid" games. That's what we're seeing across our team and that is why it's down to the manager.
3. In other fields, you have the option of quitting and joining a better place. No "contracts" to hold you. After a point, it's not the money that keeps you in a job, it's the lack of an incentive to quit (not the external incentive to join; the internal reason to have your CV in the market in the first place).
Anyone with any background in management will tell you of the old truism, "when a whole team is under-performing / seeing high attrition, look at the manager". As I said, poor performances from good players are always a symptom of a greater malaise. When it comes from many, that malaise is no longer "individual" to the players.