However, we have always had better players in those positions and Grealish has done nothing to suggest he could even get close to usurping them. He does have good control in tight spaces...(so does Doku, Sane Savinho, Oscar Bobb, Bernardo, Foden, David Silva, Berardo Silva and Mahrez - all equally as good if not better in some cases).
Excellent at bringing he ball from deep - unfortunately he had KDB, Gundo and even Kovacic who are better than him at this.
Vision to unlock defences - sorry - Ive never seen this from him on a regular basis...you dont have to be in a central position to make those passes - this supposed attribute is a not accurate...he is not good at unlocking defences and is worse than any of those mentioned above and others.
Leader? Kompany was a leader, Dias and Rodri are leaders. Gundo as well. Ive seen nothing to suggest Grealish is a leader of any sort
he is good at holding onto the ball, buying fouls and slowing the game down and helping maintain possession - but so are many others who have other skill sets that Grealish doesnt have
The reason we have not seen him in the central role is up to this season we have had way better than him for that central role. He has been lucky to be part of this team imho and many other players could have played the role he has.