Dembele's ceiling is very high. That's why most want him or Mbappe.
The good thing about those two is that Messi and Suarez still are here, so they can grow under their shadow
neymar
.
Dembele is going to leave Dortmund and join a big team next year anyway. So will Mbappe who is definitely going to join Madrid next year if he stays at Monaco this year.
They're not going to replace Neymar's output right away, but we might play far more fluently as neither of those two are ballhogs who takes 5-10 seconds do something whenever they get it.
Get one of those, or both + a midfielder who can help create something from the midfield.
Both are still raw, but both had great seasons last year both in domestic league and the Champions League, and at that age, it's quite special.