Jamdav, imo there's a bit more nuance to the Dembele argument.
So the first assumption preceding the premise of my argument would be that Xavi is a poor manager who struggles to coach cohesive offensive patterns of play. It's all a bit disjointed and static tactically. Not a fluid free flowing progressive passing game.
So now we come to Dembele. Has Dembele been a success at Barca? Fuck no! But does Dembele possess a specific set of skills which very few players have? Hell yes! Dembele's ability 1 on 1 with his explosive pace and dribbling skills is amazing. He can carry the ball and get you up 20 yards in no time with this.
This attribute majorly helps the static style of Xavi. Since Xavi is weak at coaching proper penetrative Football, he heavily relied on Dembele to get the ball up the pitch. That solved a lot of coaching problems for Xavi. That's why Xavi loved him.
Now, without Dembele Xavi is in big trouble since he has no clue on how to get up the pitch organically and invade into the final third. He'll rely on a bastardised half-effective counter pressing system to get into the final third against half-decent teams.
So, even if you classify Dembele as a bum he had a big role in this system and unlocked a lot of problems Xavi faced. None of Barca's other wingers can do that.
