It's perfunctory. Would it be a fair criticism that the time travel in TGWLTT wasn't explored thoroughly enough? Or how the future society wasn't elaborated upon? No, not really. She can travel through time. He comes from a crappy future. That's all you need to know for the drama to unfold. Everyone has their own threshold for "how much exposition I want". Not meeting those thresholds is not the film's fault, it has other problems, but it's great film overall. Lack of or an abundance of exposition is almost always a personal choice.
Hosada's film are actually a very good point of discussion here. How much exposition did
Wolf Children Ame and Yuki have, concerning one of the central plot devices, really? Almost none. It's immaterial to the core of the story which is about a single mother raising children. We don't need to know how they transform to see what it does to their lives. We don't need to know where their lycanthropy came from to see it's ramifications on their sense of identity. They could be half-aliens or half-demons for all it matters. The story would be indistinguishable, the only thing that would change are some of the aesthetic motifs.
How would the themes and drama of Life is Strange have been advanced had Max's time travel powers been explained? I have no idea. The only time travel stories for which this approach makes sense are earnest thought experiments about the ramifications of time travel, in which the mechanics and consequences are the real focus and characters are secondary. That's not the case here, despite what the game might have led you to believe. It's the central mechanic because it's a game and the game demands some element of gameplay.
But being central to the game doesn't mean it's central to the story. I don't see why that's so hard to understand.
RE: The dialogue thing. It's pretty interesting how divided people are on it. I think it's important to keep in mind that your teenage experience is not the only teenage experience in the world, and the Northwest is not a homogenous culture. What comes off as try-hard for you might have been nostalgic for someone else. At the same time, youth culture shifted rapidly within the last few years because of the rise of smartphones and social networking. What you consider "teenage banter" is already very out of date in this world of instagrams and snapchats and what the fuck ever. Yes, it is possible that it's we who are out of touch, just like our how parents looked to us when we were younger.