Jack and Doku are complete opposites. Jack is a 4-5/10 in dribbling and getting to dangerous positions with the ball and a 8-9/10 in decision making (only because his shooting skills are non-existant). Doku is a 10/10 in dribbling and getting to dangerous positions and a 2-3/10 in decision making.
The thing is, decision making is improved via more experience and game time (as long as the player wants to improve and learn). If Doku doesn't improve that by the end of the season, I would start to become worried, but right now, Doku can be world-class if he improves those aspects (a big if).
Many seem to doubt that a 22 y.o. can get better than he currently is.
Maybe they should be reminded that Grealish was playing in the Championship when he was 22 and scored 3 goals in 27 apps.
Jack got a lot better after that. Nobody really knows, but if Doku improves as much as Jack did between 23 and 25, he'll be a great player. Only time can tell.