The system doesn't suit him for England. The problem is that England don't really have any proper attacking plan other than "keep it tight at the back and let the attacking players do their thing." That means that players that take a man on like Saka, or previously Grealish and Sterling, look good in this system. I wouldn't be surprised to see Eze shine too. Whereas Foden excels in City's intricate passing around the edge of the box with his weight or pass, vision and intelligent movement. Being out on the left for a team that has none of those, and a full back who can't overlap, just doesn't work.
And all of that stems from the fact that Southgate doesn't trust two 100 million pound midfielders to run things without having their hands held. Every pundit going said they'd play Rice and Bellingham, with three players ahead of them. But no, Southgate has to get TAA into the team in a position that he has no record of playing successfully. Rice is one of the best DM in the Premier League, Bellingham is one of the best all round, box-to-box players this season (yes, I know he played up top for half a season), and Foden is the PL player of the year playing just behind the striker. Three of the best players in world football that could easily all be played in their natural positions.
Meanwhile, he's desperate to use Alexander-Arnold, yet too much of a pussy to play him instead of Walker. Don't get me wrong, I wouldn't play him ahead of Walker, but it just sums up how cautious he is. One of the best attacking footballers in the world, but he will only play him if he can have another full back on as insurance.