You don't need Gnabry to tell you that
Tuchel has said already that Dembele is the best natural talent he has even coached.
But even that's not enough for BF 'scientists'. A few here have even claimed he is not good at dribbling.
That's how objective their assessment of football is
Well dribbling is a fairly broad term, I think his dribbling is incredibly inconsistent and only effective in particular situations compared to lets say someone with better ball control eg Messi
Secondly natural talent alone isn't enough to be a successful a football player and that's kind of his issue, him not being professional enough, mid-low tier coaches during his development and several long term injuries has really set him back. We just need to look at someone like hatem ben arfa who was amazingly talented but wasted it.
For me his biggest issue is the reading of the game, he just doesnt know what to do and when to do it and a big part of the lack of development in that area is due to factors mentioned above. I've already said for the money we will not be able to replace him, but like you id rather him leave if we're going to be appointing more mediocre mangers instead of lets say a Ten Hag