> Aarch64's ecosystem is huge

ARMv8 hardware (other than Apple) only shipped 3-6 years before RV64GC/RVA20, and ARMv9 is only about two years before the equivalent RVA23 -- at least in SBCs/Laptops. Obviously ARMv8 hardware went into mobile devices a lot earlier, though it was often running 32 bit code for the first few years.

It's nothing at all like the maturity lead x86 has over both.