Milan have done a really good job by taking advantage of Juventus' bad form recently. They are at the second position now after this. I find their productivity quite decent this season compared to their nearest opponents like Juventus and Bologna. The main problem is more related to Milan's defending. They have conceded 33 goals in 29 games. 
They can actually solve this problem by transferring better defenders this summer. They spent 100 million+ euros in total for transfers last summer if I'm not wrong. They should focus on their defense line more next time they make transfers. If they conceded much less goals than this now they could have been in the title race.
You can say yes and you can also say no, but it is true that Milan have been good at catching up with Juventus when Juventus have experienced a problem in their team that makes them unable to stay besrasing with Intermilan who are at the top of the table. They can actually solve this problem by transferring better defenders this summer. They spent 100 million+ euros in total for transfers last summer if I'm not wrong. They should focus on their defense line more next time they make transfers. If they conceded much less goals than this now they could have been in the title race.
It is quite sad for Juventus and even though in the last match they could keep up with the attack from Inter Milan last week, it was good enough rather than getting defeated.
Milan are bad about their defense, but it seems like they haven't found a suitable candidate for a strong defense, but it's not a good thing to focus on defense, their central midfielders are also not good in my opinion, several times there is always a miss of communication and maybe need a central player in midfield so that it can connect between the back to the front line in building an effective and efficient attack.
AC Milan actually needs to improve in all parts of the field to win a Serie A. But for now, they have to start with improving their weakest part, their defense. Their Goalkeeper Maignan is a good goalkeeper. I don’t think the problem is with him but with the Centre backs. If the manager can get a good amount of budget and build the squad after getting 2-3 signings, the team might win the Serie A next season.
As for Juventus, I think it is just a temporary bad form from them. They will bounce back I'm quite sure.
They had been under very bad performance in the recent few seasons and were far from their glory days. But now they look like they have found the path of comeback. They are still far from the European Cup, but it is good to see that the Serie A teams are slowly getting back to their glory days.
Regards
Duke