I also don't understand that point of view. People are looking at only what happened at the end. Yeah it wasn't a good ending for Inter in the Serie A and Champions League. But these guys were still one of the most successful 2 teams in both tournaments. 
Actually nobody can dispute Inter Milan from being a successful team even as they missed the two trophies and they wouldn't be far from the third best successful in the whole Italian league currently and there potentials has not left them yet because they would always go to every season with confidence of what they have and could give, actually even if Inter Milan was messed up by PSG but from the clubs they sent home before getting there they're definitely a successful club but just like other teams has ones fall and rose to become champion, Inter Milan will not be exempted from it because they might also rise again to winn.But still we shouldn't forget how good this team has been throughout the season. Only the finish was unlucky for this club.
But in my opinion, Inter Milan's loss and misfortune at the end of this season is not because they lost in Serie A or lost in the Champions League. but in my opinion, Inter Milan's unlucky thing was when they lost their coach at the end of this season.