Looking again, I feel what City wanted when they bought him was a squad player who may come in to unsettle one of the starters. IMO, every player starting ahead of him in that team is a real talent. No doubt Jack is really good, but some players who are really good can only shine that star in "not so big teams". What City wanted him for is similar to what Klopp has with Jota and Luiz Diaz.
Again, because Pep loves to experiment with his teams, you're almost never guaranteed a starting spot as the style he may want to play may not fit your own game.
Players need to look beyond the money and club name when making transfers. They should look at how it'd affect their own styles and careers.
I agree with you and for a squad player, 100 million is a waste of investment if he won't even guarantee 20 goals a season.