But where are you going to find an Nvidia GPU with 128+ GB of memory at an enthusiast-compatible price?
Some Chinese sources sell modded Nvidia GPUs with extra VRAM. They're quite affordable in comparison to even a Mac Pro.
and let alone competing on the energy consumption!
That might even be true, but how large is the TAM for such machines?
Where are you gonna find Apple hardware with 128GB of memory at enthusiast-compatible price?
The cheapest Apple desktop with 128GB of memory shows up as costing $3499 for me, which isn't very "enthusiast-compatible", it's about 3x the minimum salary in my country!