OK I will take a stab at this, but I am going to keep this short as I don't want to go into a detail explanation for which I need pictures and video to explain.
let us first discuss why Jack was bought, it was made clear from our tier 1 that our board wanted someone to fill the role of bernardo when he was threatening to leave and that txiki was in love with Jack because of his ability to keep and move with the ball. and in the first press conference when pep was asked what he liked most about Jack? what he said was that he liked his ability to slow down play and bring others into play.
next let us discuss what Jack was doing at villa he would usually take the position of a wide player when he is in the middle of the pitch away from the box and then the more he moves with the ball and carries the ball he will move to the center of the pitch when he is near the box and then lay of the ball or make a through pass on the run. In contrast when he plays for us he is put in a complete opposite position when he is staying high and wide like a traditional winger which was never his game so makes no sense.
what are his strengths? It was universally acknowledged his best attributes was carrying the ball into the box, making space for others and bringing them into the game and also being press resistant when the opponents tries to get the ball from him. ask yourself where this characteristics are used? it surely is in the center of the midfield.
what are his weakness? beating a man for pace or trickery and putting in accurate crosses for 5'7 players or having a leather striker instincts are not his game. for a forward player these skills are essentially and why the fuck is Jack playing there?
take last night as an example why the fuck not put Jack in LCM and move gundo to false 9 and foden to LW this will make better use of each other's skills. as someone else said the only reason I can think of is that pep does not trust his positioning and defensive movement and hence he is shoehorning him into the LW until he can learn. In short people need to stop asking him to play like sterling or mahrez when he is nothing like them and pep needs to stop putting him the forward line and making our attack weak. either put him in his correct position or leave him on the bench.