So to get everything out of the game, you need to play it three separate times, yeah? Once with Duran, Angela and whoever, once with Kevin, Charlotte and whoever, and once with Reisz, Hawkeye and whoever?
Pretty much yes. It's not mandatory but there are 3 big main plots.
The fact characters and classes change their gameplay helps keeping it fresh.
The general quest is going to be the same, collecting beast powers and saving the mana tree, but the beginning point and final act vary, on top of character interactions obviously.
They added a new epilogue chapter with classes tier 4, and a new game+, we're not sure how it works yet.