I agree with a lot of what you say, especially in regards to Bernard, Schneiderlin, Kean and DCL, and even Digne, who has been poor.
But Pickford is a massive liability. These games change on small occurrences. They happen in games all of the time, like a late corner when you are 2-0 up and coasting. He comes and gets anything decent on that, or claims it, and the game is over. It wasn't a particularly dangerous corner, I've watched it back, and a decent keeper has that.
Pickford is awful at coming for crosses, 1 of his big weaknesses for me. I'm actually surprised when he catches them as it happens so Infrequently and this in itself gives team a lift every time we concede a corner, which in itself, gives us this "weak at set pieces" identity we currently have. Because the defenders don't have a clue which Pickford is gonna show up. The big head who comes and doesn't reach, the guy who stands bouncing on his line arguing and pushing a striker who Towers over him, or on the rare occasion, the level headed goalkeeper who is concentrating on the outcome of the set piece and realises if he jumps with his hands in the air, he should be reaching most things if he follows the track of the ball.
The defence has been pretty woeful since he joined, it's not a coincidence.