Grealish is never the typical English midfielders renowning for their work rate like Beckham Lampard Lingard or Mount. He is kind of slow in pace. Several years before English youth system focused on these pace and work rate heavily but Villa system I guess was not that strict.
Grealish had stamina issue in the doubt since his first seasons with Villa. But his ability to control the ball in tight spaces stood out ever since his youth career. Something rarely seen among English players. His most "English" attribution was perhaps the willingness and aggressiveness on winning ground duals 50-50 ball.
Before his kidney injury, Grealish was often subbed off early or ran out of steam in the 2nd half. During his recovery from that injury, he gained a lot of muscles and became a big lad (as Phil and Kev described). I think that it was a smart decision made by his team to maximise what he is good at: keeping procession, winning ground duels and carrying the ball. On the trade off, pace and work rate will never be the on the elite level.
Dean Smith used very carefully managed game plan to preserve/use Grealish energy by stages of the game. For a period in last season, Villa often unleashed in the 2nd half. Grealish was not lazy or unfit - his covered distance was high (>10km avg in Villa) and did a lot of ball carrying and winning the balls. His energy distribution though a game was closed to stretching to the limit.
This is not a secret at all and Pep must have studied Villa's game as an opponent.
Thus it is very interesting to see how Pep will transform and improve Grealish - a talented footballer with nature limitations.
--
On a side note, as a long time Three Lions fan, I hold high expectation for him and Phil. England team have so many high work rate high pace players but lack of ball carriers who can control the ball in tight areas to be able to set the pace of the game. Exactly what we need for so many years and lost again and again. Thus I am very happy Pep gave them a lesson.
