While I’m not really an expert on either, I have looked at code for both and I got the impression that RISC-V’s “simplicity” is actively harmful to making it a good ISA outside of teaching because it’s instructions are just not really all that great; indexing into an integer array (for example) is a shift, add, then load while basically every other architecture can do this in one instruction. It seems to me that the ISA is really designed more towards being pretty than being practical.