Don't search further... OpenGL v2.1 is the absolute minimum for the viewer, and since many things moved to shaders and OpenGL v3+ over time, it is no surprise that the rendering quality is just barely acceptable with OpenGL v2.1 nowadays.
When you use old stuff, you can't pretend getting all the bells and whistles that new stuff offers...
As for the particular distortion seen, it could be specific to the driver (try an older (yes !) one) or the graphics card itself (ATI/AMD is not the best brand for OpenGL compliance).