Sure, Barca fans dream that, after he has an great game, this is gonna be the start of a new decade of dominance. Like when Dembele had a great game, we all said, that's it, now this new Dembele is gonna take over. He finally matured and gonna storm Europe.
Then 2 games later he trips himself and misses an empty net. Rinse and repeat. After 2-3 shit games, 2-3 months out, he comes back, he has another great game, and it's Groundhog Day time again. Before you know it, 4-5 years pass.
These are not top players. These are players top teams don't want to deal with. This is why they can be loaned by Barca for next to nothing.