It's time.
We are used to loans and fairly disposable players at championship level. If you sign someone at that level, you expect them to be able to be decent out of the box. Often they start good and get worse. We are used to only really giving time to youngsters.
But at PL level, players often need a lot more time to come good.
Look at the players who have been totally written off by some on here
Awoniyi
Wood
Origi
Williams
Tavares
Hudson-Odoi
Omobamidele
Sangare
Toffolo
Who have I missed?
I don't think there is a single person on here who hasn't written off at least one of these. But they just need time to get the handle on the league