Jadon Sancho - Chelsea (loan) watch

While I agree on the "know the kind of player you sign", I think it is clear he should be doing much better even in a less favorable tactical setup. Sancho possesses skills that should work in isolation as well. When you see his game against Atletico, you see that he's not "just" a pass and go player but is also explosive and hard to defend in one on ones. He's also excellent in tight spaces and has brillant body feints in his repertoire. United didn't make it easy for him but he still should have done much better than he did in the end. IMO the only explanation for this is something mental and related to his self-esteem. So the fact that he only works to a worldclass level under very specific circumstances can definitely be held against him.

There used to be more "confidence players" like this when football was a bit less professional. From the top of my mind, Kaká, Fernando Torres and Fabregas also fell off a cliff after leaving their "comfort zones" at a scale that couldn't be explained with physical decline alone.
Yeah can get on board with that.
 
Both were fine, but we really wasted Mata by using him wide.

Yeah, we can only blame ourselves for not getting the best out of Mata. He was an elite level #10, and in the correct setup, he could've thrived. We should've phased out Rooney much earlier and let Mata and Kagawa take his place centrally.