Preseason matches are not a benchmark for being stronger in the next season, but being able to beat two great teams like Man City and Real Madrid will certainly have an impact on AC Milan players as a whole, especially regarding the players' mentality which is getting better. In my opinion, it's not just Real Madrid and Man City who play young players, but AC Milan also plays young players in preseason matches. So even though preseason matches are meaningless, preseason matches are very important to start the league well. The next preseason match is against Barcelona, if AC Milan manages to beat Barcelona I think next season AC Milan will really be a tough contender in the fight for the Serie A trophy and the UCL League.
What is clear in this match is that they are only conducting trials for each team and I am sure that Real Madrid will not use the players they used in this pre-season match. Manchester City and Real Madrid will use their main players who are stronger and their mentality is no longer in doubt, but I must admit that Milan's performance was quite good when they beat Real Madrid and Man City, they are trying to use various strategies to prepare for next season.
It is no need to explain again indeed that Milan has always been a strong competitor to win the Serie A scudetto from year to year with its tough rivals Juventus and also Inter Milan.