Different things are being asked of him compared to his role at Villa.
He still has the same talent but Pep's using it in a different way.
If he'd gone to any other club in the league, maybe any other club in the world, he'd look roughly the same player he did at Villa, doing roughly the same role.
At Villa, he was sharp, strong, direct, and so dangerous in fast-paced attacks/counterattacks. A manager looking for a player to play that role would see the price tag Villa put on him, because of his enormous value to them, and would set their scouts to finding a "Grealish-type player" at a lower price. Because the skills needed to do most of what he did at Villa would be available at a lower price. It's not something every player can do, but there are options.
But Pep saw something else in Villa Grealish. When we bought him, articles at the time said Pep had been asking questions about him for a long time, specifically around things like what positions can he play.
There's a rare combination of skills in there - the close control, the way the ball sticks to him, la pausa, the unselfish passing instinct, the way he carries the ball, the gravity drawing opponents to him, probably dozens of other things Pep sees that I don't, and Pep is honing those skills to mould him into a player that fills a much more specialised niche than a traditional winger.
I don't think he's the answer to all our problems, it's a team game and one player can only influence so much, but I do think it's telling that many of our most chaotic matches, including the last couple, have happened in Jack's absence. He gives all his teammates around him time and space, and that makes things easier.
I think bringing him on for Phil at half-time against Bournemouth was less punishment for Phil not passing to Haaland than a wish to use Jack to keep the ball, slow the pace and help the whole team conserve energy in an already-won match. And Pep's comments after the Newcastle game made it clear - we missed the way Jack helps the team control the tempo, and that meant we played far too much at a pace that suited Newcastle.
Not every player's style and skillset suits every game and every opponent. But Jack will get plenty of game time when fit this season because - although he's still learning, and like any player he has room for improvement - he's proven to Pep that he can play that role, and play it well, and do it in a way that helps the team function at the top of its abilities.
It may not be as exciting to watch, or as likely to lead to individual accolades, as what some other players can do on the wings. But it's an incredibly useful option for us to have.