I still like the Aaron Ramsey comparison - ridiculous engine, big contribution in the final third for a midfielder, but not really clear he has the tactical discipline, technical security, and passing range to be a great fit in a double pivot, especially in today's tactical systems. Tuchel's two CMs are often tethered together only a few yards apart when out of possession and not pressing high, they move in tandem and they are pretty selective about going forward in transitions. The primary role of the position is to help control matches with and without the ball. Maybe Gallagher could learn but I've never seen him play on a leash like that. At Palace he is just all over the place like an attack dog.
For me, Jorginho is the most natural partner for him on the squad. It would be hard to see him playing alongside Kante as both naturally want to push forward.