[CyberDildonics]

> Yes, but rendering is a shader on a bunch of those buffers right?

No. Tracing rays is fundamentally a sorting problem when dealing with the acceleration structure. Rasterizing samples means accumulation of values and weights, which means either atomics or separate buffers (and if you are using the GPU creating a buffer for every core is out of the question). You could sort the samples into buckets and rasterize those separately, but you are again faced with GPU partitioning at the very least.

There are plenty of ways to use the GPU to do all aspects of rendering, but it is not even remotely as trivial as you are making it out to be.