~Snip
After all, playing in friendly matches too, each player will certainly not play with maximum gameplay, because to avoid injuries too. So yes, friendly matches are basically not to get a win, because winning won't affect their ranking either, right. So, playing in friendly matches is at least to provide opportunities for all players to play. At least, to strengthen teamwork and also to maintain fitness, of course, so that they are better prepared to start matches in the actual match in the new season. So, this defeat by Arsenal I am sure, certainly does not make a bad view on Barcelona.
Even if your assumption is correct, Barcelona's defeat to Arsenal with a score of 5-3 will be an object of ridicule for some people who hate the Catalan team. I agree with your assumption that friendly matches are nothing more than test matches to give players a chance before the official competition starts.
After all, friendly matches are not matches that are so important for all teams, let alone to play as much as possible. It's hard to expect friendly matches to be very interesting because players tend to play it safe to avoid injury, but the result of the match will be judged positively by each coach of the two teams. Next match, Barcelona will face Real Madrid for a friendly match at the AT&T Stadium in Arlington, Texas, United States.