To be fair, it's a stupid time for Jack to move.
If he continues on the same trajectory, he can make this move if the Villa project fails in 12/24 months. He can get his £100m move to City at 27years of age, nothing will stop him.
If he gets worse and fails to start at City, or Villa get CL football, he would have been wiser to stay.
So if I was Jack I'd demand 200k a week and stay at Villa at least until 2023.