I think FF13 reeaaallly could have benefit from more character interaction, but too often cinematics were about fleshing plot and the "teen drama" among the characters.
That's the point... big part of the narrative (so far) has been focused on the mythos because that's what everything comes down to.
I don't know about the teen drama part in your post though. I know what you mean, but I never got that the drama in the story was superfluous. In what I think XIII failed though was the way a big chunk of that drama was presented, I'm not saying that is bad but I understand all bitching and moaning that there has been with fans feeling so bothered by the story and characters in the XIII series.
The entire story is told in a very Japanese manner and it doesn't feel as "universal" or relatable as how themes are presented in some others games in the main series. Personally I don't mind but I would like to see Final Fantasy XV bringing back the weight of drama backed up by the scenario and the characters, not just having it there for the sake of it.
Though just to be clear I do think there are parts in XIII and XIII-2 that have a good balance in their drama, but most of it is just there to keep the tone of the narrative going.