That may be it. Renderman is of historical interest because it introduced shaders to the industry.[1] That's where the look of Pixar's early work comes from. Everybody else texture-mapped photos of the real world, or 2D paintings, while Pixar was generating infinitely fine detail with shader programs. This allowed the camera to get close to objects without the textures going blurry or blocky.

Today, shaders run in GPUs, and everybody does this, but in a different way.

[1] https://en.wikipedia.org/wiki/Reyes_rendering