If pre season can not be used to determine how a team is likely to perform when the new season begins then how are they able to know the players that are going to be starting in a game for the season? We understand the difference between the tournament and the pre season games but a player performance during the pre season is used to determine his performance in the league since the players performance in the training make the coach to start them in the match so I believe a player who is not feet during the training and pre season games will not be given the opportunity to start a match during the new season.
The main reason for pre season games are for warm up and testing of new formations because of the recent players that joined the team. It is not a means to choose who would start when the season begins. Also, coaches can use the pre season matches to evaluate each player readiness and fitness for the upcoming tournaments, but that is not enough reason to choose a line up. A lot is consider for that, it ranges from chemistry, past performances, tactical ability etc. And yeah, most young players are giving the opportunity to show how well developed they are to play in the big team.