Grealish isn't as nailed on a starter for big games as he once was. I agree that he'd most probably start him over Doku in another CL final but I think it's mainly because Pep knows Doku is a good impact player to bring on who can make things happen, just like he did in the FA Cup final. I agree that Jack gives us more control, I also agree we're less open to dangerous counter attacks and he creates for players around him. I also think Jack should be more creative for himself by beating his man, by crossing the ball and by being more direct on goal.
Doku makes mistakes and can not hold onto the ball as well as Jack but he's not as experienced. But he's less predictable, tries to make things happen and more exciting to watch, and watching exciting football is a big reason why I pay my money and go through the turnstile.