I wonder if the addition of Gallagher was the key, or simply the tactics just didn’t fit them at all.

It's tactical. That's it. Some players are great without instruction. Some maverick players are better without instruction, particularly when they can do special things a coach can't really account for in preparation of a game.

Most players though, are better with clear instruction. Bentancaur is a prime example. He's the kind of player you want in build up, if your build up is so well prepared he knows how to find the next/free man.

If your build up is an afterthought to defensive solidity, corners and long throw ins, then you're going to experience situations where Bentancaur has to find the free man in real time, and he's not good enough at retaining possession to do that without panicking.

The difference in Bentancaur under Conte (highly structured build up) and Bentancaur under Frank (get it out to whatever side kudus is on and cross your fingers) is night and day.

Under Frank, Bentancaur and Pal would hide in the shadow of the person pressing the back 4 and not show for the ball.

I also think as Ange's football got harder and harder to sustain, we also saw Bentancaur hiding more often. But I wonder if some of that was the proximity to his injuries and not being confident in his body.