Grealish hasn't met our expectations. I think that this is uncontroversial.
Grealish excels at drawing fouls and keeping the ball. He's not great at beating defenders one-on-one at all. And he his crosses aren't exceptional. Since we mostly play Grealish at left wing, the aforementioned weaknesses in his game come to the fore.
On top of this - Grealish likes a "night out on the town." Pep doesn't tolerate this behavior - and this sets up a tension - where Grealish is in the dog house under Pep but might well start under a different manager.
IMO - the best outcome for Grealish - is that we sell him this summer. Under a more tolerant manager he'll start more often. And, IMO, left winger isn't at all the best position for Grealish. An attacking midfield role on the left side is a much better fit.
He's not met the expectations when you pay £100 million, that's on the club and those involved.