You surely mean "history tells us that the cheapest and largest-volume ISA is the one which will become the highest performance one".
It's not "RISC" having reached x86 levels; it's ARM variants. They did so with volume that for the first time in modern computing massively exceeded x86's. Apple's PA Semi acquisition has resulted in wizardry, but that wizardry would not have been possible without the massive volumes TSMC enjoys.
In any case, I'm not convinced that the above is sufficient; there has to be some level of technical superiority (or at least reasonably equal-level) as well. Otherwise, some inexpensive microcontroller that is manufactured at 100X the volume of x86 would have taken off. Does RISC-V have enough "goodness" in its design? I do not know.