AMD's MI325 is slower (maybe 2x slower) than Nvidia B100. Sure it's cheaper and maybe consumes less power but you need more racks, more networking, and more labor to get the same performance.
The B100 is only 20% faster than the H200 on average within the same target accuracy. There's nothing revolutionary about this architecture, that's why it's 4nm.
Nvidia drops precision and adjusts via software to sell a new gen.