The first thing that comes to mind here is, "hey maybe the problem is that we are rendering our scene in the middle of nowhere. If we had a proper environment, the lighting would be much better..." So, here is the same render but with an envsphere (from BB.) The lighting is now better although very blue. BTW that's another common problem that arises because most 360 pics like this have huge skies and that turns everything blue-ish. But this is fixable by editing the pic or finding different ones. A bigger problem is that while the artifacts are less, they haven't gone entirely. There are also some new artifacts in a few places like those bright splotches at the small bump in the floor.

 

What else can we try ? Read on...