It's like England saw how Michael Bracewell did this summer, got confused and thought "we need one of those"Will Jacks has a FC bowling average of 53.
I guess the difference is that all of Will Jacks' fundamentals for bowling off-spin are absolutely top-drawer: he's got height, he pivots beautifully over his front leg, and he's got big hands so he can really rip it down the seam and get proper turn. Essentially there's no reason why, with just a year or two of work, he couldn't be one of England's best spinners. All that he really needs to do is to properly groove his stock ball and develop two pace/flight variations that he feels confident enough to go to regularly.
I'm saying this from the perspective of someone who went from never having bowled an off-break in anger to getting paid to bowl off-spin in the space of less than a year, so I know it can be done to a reasonable standard. Applying that logic to Test cricket is a gamble, but there's no reason that with enough support it can't be made to work.
Whether it should be made to work is another matter, as it shows a complete lack of confidence in the likes of Amar Virdi, Dan Moriarty and Liam Patterson-White - but Will Jacks is in the side now so he's the player I'm analysing.
The final thing that I'll say is that a lot of spinners, especially finger spinners, suffer from the perception that a wicket (for example) bowled through the gate has more value than a wicket caught at deep mid-wicket. They both count exactly the same, and there is an element of skill in forcing the batter to mis-hit you. If you can deliver a ball with overspin such that it dips and the batter misjudges the length then that's a wicket you've earned. If you change your grip slightly so that the ball comes out slower with the same arm speed, then again that's a wicket you've earned. If the batter is frustrated and aims a big shot at a ball that's not quite there for it, that's a wicket you've earned.