For heat haze textures to appear to produce the desired undulating effect, something needs to be moving. Can be the observer, the heat haze texture, or whatever is behind it.

The plat23 heat haze texture has a tcmod scroll so the distortion pattern changes with time, even if you are standing still. This does not work as expected with material system enabled. If you stand still, the background is distorted in a fixed way that does not change with time.