No chance Necalli is the final boss. You don't reveal a final boss that early and not make him seem like a final boss.
Yeah, on top of being low poly, they are animated very poorly. I can see the animation getting optimized before the textures for some reason. To your other point, we know "weather" is supposedly a thing, so if it's actually dynamic then the reason the background assets are so poor right now is to allow for the weather to work. They may be going for whatever it takes to get it running first, then work to optimize it leading up to release. That's my wishful thinking.