As for Inter, they didn't invest after winning everything so they repeat Milan's mistake and now they aren't as good. Their squad is very old and they buy some mediocre players at the moment.
Disagree with that, Inter still have the best team in the league IMO. Benitez was clearly the reason why they've underperformed in the first half of the season.
Right now they're on the right track, if they beat Cagliari tonight (which is most likely gonna happen) they'll be just 2 points away from Milan which is practically nothing.
Milan took advantage of Inter's poor form in the first half of the season and they found themselves at the top of the league. Now with Inter closing in I really believe that Milan will slip further and further and eventually Inter will win the league.