Manchester United has played friendly matches with Laliga team Cadiz yesterday that surprisingly they were lose from Cadiz with scores 4-2 although some of key players such as Martial, Mctominay and Van De Beek were played but Manchester United cannot able to beat Cadiz who filled with young players and Manchester United will do one more friendly match against Real Betis this Sunday before playing at Carabao cup against Burnley on round of 16
Opposite result was happened to Arsenal that playing at Dubai Super Cup against Lyon they can able to win with big scores from Lyon with scores 3-0 although Arsenal was playing only with young players but they can able to performing well on that match
Friendly matches cannot be used as a benchmark whether the team is good or not many use friendly matches as a warm-up only, you remember before this year's season started Man United won in several friendly matches but their appearance was different when they competed in the League, and friendly matches as well as the tournament you mentioned are very good for young players for them to play and synergize with teammates.
Yes, I agree that friendly matches are only a warm-up event for the players before restarting the real league. It would not be surprising if a big team could be beaten by a team that could be considered weak, especially since most of the players in this match were players who didn't have many chances to play in the Premier League. We will see the real strength when the main players have joined. Many teams are taking advantage of this long holiday to hold trial matches and in my opinion it is a very good step taken by the relevant team.