I've not seen a single person claim that. As mentioned before, there was the Madrid match last season where we were pretty dominant. The year before that, there was the 0-4 win against Dinamo Zagreb (small team, yes. But dominant where we would usually struggle), and then before that there was the 0-3 against Dortmund.
He has 4 goals in 10 games this season, our joint second highest scorer on level with Dybala and behind only Ronaldo with 5. I'd say that's a pretty good statistic in his favor at the moment. He also has two assists (equal to Cuadrado) and, per whoscored.com, a total of 9 key passes which places him right behind Cuadrado as the next highest with 11. So to summarize, just by the statistics, we would have that threat in the box with minimal, if any, reduction in chances created.
You're greatly downplaying his performance for us this season.
As would be expected of him being as he has played in every position on the right side during that time, he should be leading in those stats. The point here is whether or not we would've scored more. I truly don't see how you come to the conclusion that we would not score more by utilizing a man that has scored 4 goals in 10 games this season while still providing some level of creativity up front to create different types of chances by having a different structure up front (better hold up play vs Cuadrado crossing). But you seem to be stuck in your opinion and again I will say continue to downplay his performances for us this season, so I will not engage any further.
That said, my dream is still a frontline of Ronaldo - Dybala - Bernardeschi.