I have been given some equirectangular projections from blender to visualize in VR. The rendering was done from within some 3d model. The horizon is almost like an S, so when I project it onto a sphere the perspective seems a bit off. Is there anything the blender guy can do to produce a flatter horizon, like restrict attitude of the sphere etc)?
I haven't had too much experience with equirectangular rendering in Blender, but as a photographer I can say that this happens in real life when the camera is not level, so perhaps check that they have their camera rotations all set to 0. I was able to straighten it using a pitch of 30º and a rotation of -2º:
I could be wrong, but it looks like you haven't UV unwrapped the sphere. This tutorial explains the process well.