He didn't really play winger though.
I don't think that particular idea was that bad, Koeman often seems to work with dream scenarios and don't work them through enough, he seldom gets it all to work together, but I can see the dream scenario here. He is closer to put pressure on the defence, and to connect with Depay and catch crosses, he should also be an option between the lines a lot more, the thought was probably that Busquets and Nico would be able to serve a lot of balls to him and Gavi in the half spaces and that Coutinho too would be able to combine from there.
Frenkie is not at all an incarnation of Barcelonas DNA, every canterano midfielder and most defenders and attackers have a better understanding of the basics than he does - when to move towards to or away from the ball, when and where to take the ball at all times etc.
Frenkie of course have many advantages, but at the centre of the pitch he is a bit ineffective and unelegant, compared to those who spent years at la masia.
I remember one of his first games for Barcelona, when he was put as an interior, but by himself almost played like a winger, getting out towards the touchline in order to get the ball, it was a bit telling to me.
My own dream scenario is him playing CB, I think he could be great there but he has a few weaknesses that he needs to work on then and I think he'd need to focus for a while to get rid of these habits.