https://icircuit.net/benchmarking-raspberry-pi-pico-2/3983

The Hazard3 cores was designed by a single person while the ARM Cortex cores were presumably designed by a team of people. The Hazard3 cores mostly outperform the Cortex-M0+ cores in the older RP2040 and are competitive with the Cortex-M33 cores that share the RP2350 silicon. For integer addition and multiplication, they actually outperform the Cortex-M33 cores. The Hazard3 cores are open source:

https://github.com/Wren6991/Hazard3

That said, not all RISC-V designs are open source, but some of the open source ones are performance competitive with higher end closed source cores, such as the SonicBoom core from Berkeley:

https://adept.eecs.berkeley.edu/wiki/_media/eop/adept-eop-je...

As for the other problem you cite, the RP2350 has both RISC-V and ARM cores. It is a certainty that if the ARM cores had not been present, the RP2350 would have been cheaper, since less die area would have been needed and ARM license fees would have been avoided.