Simeone doesn't play him much and sometimes even leaves him off the bench entirely. Oliver doesn't seem to be an ideal fit for Atletico's style of play, but he would be amazing in Tuchel's team. He's not a player whose greatness would be reflected in stats necessarily. He won't directly assist many goals, and he certainly won't score many himself. He's incredibly shifty in tight spaces to escape pressure. He positions himself well in buildup. He can make extremely accurate Verlagerungen and he has a very good short passing technique and timing. He's often compared to Xavi, and style-wise that's IMO not far off. At Atletico, he hasn't really had the chance to play very centrally, and their pace in attacking and general offensive buildup just isn't really suited for his talent. He's not as well-rounded as Koke or Saul, but if he finds a context where he can thrive, he has a higher potential than either of them. They have a lot of really good midfielders and wide players now who just seem to fit them better. He would be perfect as a central midfielder in Dortmund's positional play though.