You would scrap Henderson in favour of Cook?
I assumed you might have been taking the piss as you've taken my quote out of context for some reason. I'm talking about playing in a 38 game season for a Premier League side vs a 32 team knockout competition with England (like the actual English national side). His achievements with the U21s are irrelevant, that's like taking Gayle's record in the Championship as a measure of how he performs in the Premiership.
He isn't going to be a starter at the World Cup so his role is different, and as he doesn't offer anything particularly unique he's just backup for Henderson and Wilshere. Shelvey would be the same thing but with the advantage of actually being able to change a game if needed.