I believe if Xabi Alonso notices his players are playing individual football instead of team football next season, he will call them into order, and if any player feels that he's too big to follow Xabi Alonso's tactics, Xabi Alonso will have no option but to drop that particular player from his squad and use the player who will listen to him and fit in with his tactics.
Xabi Alonso has his sharp vision from his times as a player in the past and as a head coach since his start with Bayer Leverkusen. This is possibly one of main reasons why he was chosen by Real Madrid to rebuild their squad for a new successful era. They already have good players, and their squad are even imperfect but still competitive enough compares to many big clubs. Xabi Alonso if can succeed in enhancement on their existing weakness and current strength, will be able to bring Real Madrid to many titles.
Yes, of course, next season the competition between Barcelona and Real Madrid will be extremely intense, as these two teams have consistently been the strongest in La Liga every season. However, when it comes to predicting who will win the title, I think it will be very difficult to make an accurate forecast. The issue is that both Barcelona and Real Madrid currently have exceptionally strong and deep squads. Given that, it will undoubtedly be quite challenging to predict which team will emerge as the La Liga champion next season.
Both Barcelona and Real Madrid are strong, have many star players and also deep player resources, with ambitious targets to achieve in each season. They will continue to be direct competitors for big titles in La Liga and Champions League. They are both preparing for a new season with different activities on transfer market and at their clubs.
Before they play some first matches in a season, it's hard to predict which club are more competitive and Xabi Alonso carries big hope of Real Madrid in tactical improvement in order to compete better against Barcelona. Barcelona in contrast will need to pay attention on their player resources and how their players maintain ambition and performances in this season.