For anyone still curious about the exact role of Will Jacks in this England Test team, the key is probably to see him as a kind of a tell, a set of entrails, a weather vane on the state of the game.
The first rule of Jacks goes like this. If you can see Will Jacks on your TV screen, it’s bad. If Will Jacks is bowling when you wake up something has gone wrong. If Will Jacks is batting something has also probably gone wrong.