I disagree; the pre season games does not give any picture or indication of how the team performance will be when the season starts. Instead; the pre season games is to get the players to up their fitness level; understand the weakness of the team and work on it greatly. The MUFC pre season game against leeds was good. Some academy players did well performance wise. More to expect.
You're correct. Last season, Manchester United had a great preseason, but at the beginning of the Premier League, they flopped woefully for the next two games. Losing four goals both to Brentford and Brighton.
The use of yougins tradition has been going down for a long time, the young players did blend in well with the first team players. The coach will still have decisions to make concerning player's leaving.
I don't think Chelsea will be competing for the EPL title next season, they have a lot of ground to cover before they can challenge for the EPL title again, they have a new manager, too many new players that are yet to adapt, and a 'new' hierarchy at the club that's yet to understand how football works (i consider Todd Boehly to be clueless about the beautiful game). Thus, next season Chelsea will be in the race for a top four finish, and if they can add one of the domestic cups to it (either the FA Cup or Carabao cup), then it would be a good first season for Pochettino.
They're not even ready for that, it'll take Chelsea couple of two years before they can successfully fight and compete for the the Premier League. It'll sure be a struggle for some players but with time they'll definitely adapt. I hope to see Pochetino successfully winning his first trophy as a manager for Chelsea.