Jose's system did not suit his style of play. It also didn't suit Lo Celso, Ndombele, Alli, Lamela. Does it mean they are all awful players? Son's form fell off a cliff once Jose's formation was figured out - does that mean Son is crap too?
Jose's philosophy was to let the other team have the ball and to maintain a defensive shape. Don't press the ball, sit back and wait for the other team to make a mistake and catch them out of position during the transition.
Sissoko was one of our squad that was open and said that a number of players were struggling under the system as it was very difference to how they played under Pochettino and they weren't adapting.
Under Poch we preferred to control the game. Keep hold of the ball, but take little risks. Build attacks slowly and focus on recovering the ball quickly. Poch's system failed as the fitness of the squad dropped with age. We often conceded shortly after substitutions, and when we lost possession of the ball during our attack formation we were too slow to get back into defensive shape.
Let's see how Nuno sets up before writing off our players.