You are right. Mutual understanding is very important in football. Because 11 players play here. If the understanding or relationship between them is not good then its bad effect can be seen in the performance of the entire team. Last season we saw Arsenal and Newcastle teams. Despite not having very strong squads, the performances of these two teams were excellent. They have been consistent throughout the season. And this is possible because of the good relationship between their players.
A team must be a united team to work together as solid as possible and when they are united, they become a stronger team.
Each player has strength and weakness and no single player is perfect, therefore with a united team, other team-mates will cover weakness of other mates and they also can take advantage of their team-mates' strength to gain better results for a team. Arsenal and Newcastle United are good examples as you brought them here. Newcastle United in this season even are making big surprise in Champions League.
In Premier League, years ago we saw Leicester City in a season when they won over many big clubs to take Premier League trophy.
Manchester United has a very strong squad. There is no dearth of talented players in the squad. However, their performance is poor because the understanding between the players is not good. Ten Hag definitely needs to focus more on this aspect. If not, it will not be possible for Manchester United to maintain consistency.
Many years after a retirement of Sir. Alex Ferguson, Manchester United still don't get their discipline in the club back. I believe it can not be achieved only by players, coach but must come from very top positions at the club. Coach must be given full power to control players in the club and coach must be supported by top members in the club.