I agree he's not a generational talent. Those are far and few. The last one was Neyclown and before that CR7 and Robben in terms of wing forwards. Messi in a different category altogether than even those 3.
For me, he showed more than Coman or Sane at the same age in his Dortmund season. Sancho I haven't seen much of so I can't comment. Sane hit the highest level out of these 3 but it helps playing under Pep as an attacker.
I guess my expectations were that despite our obvious deficiencies at manager, he would atleast play at an elite level. Not top 3 winger/wing forward in the world or anything like that, but easily in the top 10 which should be the standard for a Barca attacker. And here he is competing with Fati for a spot.
The problem with Dembele is that he's not a very efficient dribbler. I don't care about his dribbles/game stat, he's not very efficient doing it going forward in dangerous positions. His movement off the ball is awful, he's a type of player that need the ball at his feet, he's mostly stand at one place and wait for someone to pass the ball to him than run into a position to receive it. He's getting slightly better at it recently, but it's still bad and that makes him a very poor fit for Barcelona, or any team that won't commit to building their attacking movement around him.
This is why Barcelona should sell him. We don't need more creative wingers that act like CAMs. We need more direct wingers that know how to position themselves, are efficient 1v1 and can score goals.
That means no Dembele, no Sancho, no one in that mould as long as we have Messi. Heck even without Messi they're not good enough to build the team around.