It's very hard to evaluate strikers. They are dependent on a lot of variables. For sure, Kean is the weakest of the three with his ball control and general play. But the ball finds him somehow. We are sure of that so far as a Juventus player. It finds him. Is that luck or is it because he runs more? Runs faster? More instincts? Who knows.
If it takes 3 chances for him to score and it takes Scamacca only 2 chances, but Kean runs himself into more chances in total, is he better or worse? I don't know!
We need more data.
If you expand the data to include Kean at PSG and also Everton (league and cup). This also includes Scamacca in Serie B, where he scored less frequently than Serie A
The moral of the story is spend money on CMs so you always have the ball and you always put it in the opponent's box. Is it any surprise that we declined as soon as we lost our good CMs?