Some people are blind. Dembele will never be a top player, even against real he was awful, in the second half in particular he was losing the ball every time. Besides his assist for auba he was basically playing against barca.
At his best he's capable of providing lethal final balls, but he doesn't excel at the fundamentals like other top wingers (Neymar, Robben, Ribery, Mahrez) do. He always looks uncomfortable with the ball. Very erratic passing. And his dribbling is just not convincing. He can rip apart a defense with his pace, but he just won't be able to elude 3 players with pure skill and control Messi, Neymar, and Ribery were capable of doing it. This isn't me complaining about him not being elite with ball control, I think the average winger has more consistency with ball control than Dembele does.
However, his strong areas - crossing, vision, and pure pace makes him an excellent option as a utility option in an elite team. Probably the best utility otions in Europe. But as a star player, the main starting winger for an elite club? I just don't think he's that good and he'll never be that good because of his fundamental limitations. Which is why he's not worth the salary he's asking for. We should take advantage of him and then let him go wherever he wants, it's that simple.
I think he can be adequately replaced quite easily by a winger of Raphinha's level (who's far from elite imo). He's not worth the fuss.
