It is a big problem, especially in the way ETH wants to play. Brighton pressed high and United couldn't really deal with it, when the central midfield pairing is Fred and McTominay it's going to be a big struggle to play it out. Potter is meticulous in how he drills his side, and I thought he got it spot on with both his on the ball and off the ball tactics.
It's very early days and Potter is now pretty well versed in the league. You could see a lot of what ETH wants to do but it's always going to take time for him to implement these systems, I thought on the ball United looked very janky and struggled to play with any real tempo or rhythm, and off the ball they looked quite open and were getting dragged around. I thought the second half changes were good and United had a decent spell at one point, yes Brighton ceded the space but dropping Eriksen deep allowed for him to spread the ball in a way Fred can't, and bringing on a striker helped in enabling more overloads out wide.
I don't know what the current status is with FDJ, but I can see why ETH was so desperate for him.