This isn't really concept art. It's storyboarding for battle design. I'm glad they're sharing parts of their development work because few game studios do that in the run up to release - instead, they add it as unlockable material in the game, which is much less valuable to me because by then I don't care about morsels of development material as I already completed the game. But releasing stuff like this before you launch the game allows you to get fans coming back to see what you have to show, without having to invest much time or effort.