You don't win an overall market by focusing on several hundred million dollar bespoke HPC builds where the platform (frankly) doesn't matter at all. I'm working on a project on an AMD platform on the list (won't say - for now) and needless to say you build whatever you have to what's there, regardless of what it takes and the operators/owners and vendor support teams pour in whatever resources are necessary to make it work.
You win a market a generation at a time - supporting low end cards for tinkerers, the educational market, etc. AMD should focus on the low-end because that's where the next generation of AI devs, startups, innovation, etc is coming from and for now that's going to continue to be CUDA/Nvidia.
nVidia is dominant now. The question is, what's your wedge.