I think the real issue is that Nvidia is the most closed when it comes to releasing specs. With the proper specs, open source developers will produce better drivers than Nvidia.
That may be true for specific features like Optimus--I can't say. But if you're talking about writing a full 3D driver stack for a modern GPU, you're almost certainly underestimating the effort involved by several orders of magnitude. NVIDIA has hundreds of full-time software engineers working on the various parts of the GPU driver stack. Now imagine doing it without the immense institutional knowledge.