What are you trying to say, its not clear. Anyways, Dembele issue wasn't about finishing, it was IQ and decision making. Playing Tiki Taka and high defense requires self control and intelligence, thus Dembele was a horrible fit for Barca
We buy many "hopes" but hope is given by talent and prolific players show that talent from the start. You can refine many things but finishing is very hard to refine when you don't have the close quarter ball control and strenght. Neymar was the most talented skiller you could ever dream, but his body mass never allowed him to win the glory his talent deserved, 1 v1 with all his dribling was very exposed to being mauled or blocked by simple tactics.
This guy on the other hand is very strong, fast and by changing directions looks a very dangerous player, but he lacks the refined style as Dembele.
Dembele is not an idiot but very inconsistent in tight spaces because he lacks ball control. Add his flimsy body and the disaster is complete.
My point is you can look very dangerous and good but if you lack in strenght or ball control the prospects aren't that good. In my opinion what we witnessed from Nico is his prime, as was the case of Dembele and Neymar.
Neymar is a very important case to study since he had it all except strenght.
Now we should take in account your idea of football Iq, but remember most players are average in Iq and most finishes come natural. Dembele needed many times to rush the ball to compensate for lack of ability and streght. What you consider a defect in my opinion was just a needed atitudine. If Dembele had the possibility of dribling on the spot and turning players around he would have probably played with more calm.
Ability gives you time to find solutions. You can be a big brain player but if your abilities are poor you will simply lose the ball before you would have the oportunity to give a briliant pass or make a briliant curved shot.
Talented players look on average more inteligent because they have the ability to buy time in every situation. Dembele and Nico lack that. Of course you can pass backwards but then boos might come from the Catalan crowds who want you to be a hero not a cog.