Who says that Inter has been much stronger than Milan this season? As far as I can see they are about as even as it could get in Serie A with respect to both the points and the goals scored and conceded. There isn't really much of a difference between them. Inter has beaten Juventus in Coppa Italia, which I think shows that they are definitely able to beat Milan as well in the Champions League. This is a 50:50 game in my opinion. None of the teams really has an edge over the other team. Inter has a bit more pressure in the league as well if they want to qualify for the Champions League. Even though I think they can beat Milan, I doubt that without tons of luck they could also win the title in this competition.
Yes, it seems that Inter and Milan's performances are not much different, in Serie A they are also not very consistent. Maybe if you look at the performances of these two teams since the group phase, the Nerazzurri are a bit more favorites because they were able to overcome difficult obstacles. But I agree that the match between the two teams from this city has the same opportunity. It is very difficult to predict who will qualify for the final. There are several factors that will later determine their steps, such as pursuing targets in Serie A. Pioli and Inzaghi certainly have to rack their brains to be able to provide the best for their team and which targets will be their top priority.