I have not watched much of him in the Premier League, so maybe he has changed, but I wouldn't call Jacks game one-dimensional with NYCFC. He was a complete winger during his time with us. High work rate in both directions, excellent off-ball movement both down the line and cutting inside. The ability to finish and pick out a pass. Swapping Fernandez for Jack would be a massive upgrade; his off-ball movement and the timing of his runs alone would make our offense significantly more dynamic.
I doubt it happens, but I'd love to see us switch to the 3 DP model for the remainder of the season and add both Jack and a high-level DP CAM. If they prefer the 2 DP model, they can switch back next season when Martin's contract is up.