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
The friendly games are just to help the coaches assess their team's performance and progress so far and it is not a competition that the fans should whine about a lose. Soon the world cup will be over and every player will be returning back to their clubs to resume the season. Arsenal also had a game against Lyon which ended in a 3 nil win in Arsenal's favour. The boys put up a good show and dominated the game so well.
I agree with your review that friendly matches are not real competitions, friendly matches are just trials to see the performance of players who are rarely used and it is the coach's job to screen potential players, even though Manchester United lost in the trial but I'm sure it won't affect their appearance when they returned to the English league competition after the world cup, because many great teams lost during trials but they returned to play well when participating in official competitions.
Yes, that's right, friendly matches are one of their ways to give opportunities to players who rarely or never even experience playing in real competitions. And who knows in that friendly match there was a player who managed to steal the attention of a coach to use him in the competition.
You're right, there are a lot of big teams who lose friendly matches, but that doesn't mean they did the same when they started the league. So something like this is something that usually happens.