Is there an actual U.S. RISC-V CPU that achieves competitive performance? I think the performance leaders are currently based in China.

There's a difference between announcement, offering IP for licensing (so you still have to make your own CPUs), shipping CPUs, and having those CPUs in systems that can actually boot something.

For instance, SiFive in the US, but last time I did check them, their RVA23 CPUs on their workstation boards did not have cache-line size vector instructions (only 128bits aka sse grade I think), RVA23 mandates the same "sweet spot" for a cache line size than on x86_64: 64bytes/512bits.