Football is about scoring goals though mate. I will have to disagree with you here mate, as much as I love David there is imo not one thing he can do that Yaya can't. Yaya is just as technically gifted if not more so than David. He also has as much vision and equally able to conjure up the precise defence splitting pass. As you stated, Yaya also offers goals. Not just goals but big and important goals at crucial times. I don't expect people to agree with me as this is like asking whether to take the Rolls or the Bentley, which is a nice problem to have.
KDB is the future of the club. At present though as in previous times, Yaya is the one who is coming up with the key contributions at the crucial times.
It may even be Raheem that starts from the bench in the big European matches that we will hopefully have coming up and we play the trio of Yaya, KDB and Silva in attacking positions. Yaya needs the shackles taking off him and we should play to his strengths. He should not be left floundering in a two man midfield while inferior players just pass round him.