He was a kid at City, do you remember him playing in league games in March/April, or Cup semi finals, or competing in 2, 3 4 competitions at a time? No, he was a kid in the academy. He did well at Dortmund, but that's a smaller league, a smaller, club, with nowhere near the expectations, attention, reach and pressure of playing for United.
Sorry, maybe he's cut out for Dortmund, but United is a couple steps up, at least, and not every player has the ability, which in fairness he probably does, or the mental fortitude to make it at that level.
And I think my point is being made by reality, certainly a lot more than your point is being made. Have you ever seen a player have a minor dip in form, and in response the club sends him off to train privately in another country, in a shroud of secrecy, with the aid of physical and psychological experts? Is that something that happens all the time? Clearly he's struggling at United.
I understand you like Sancho, and your butthurt because people are criticizing him, but that's the reality of life. If you can't handle your favorite player being criticized when they don't perform than maybe the internet isn't for you.