I’m not as experienced as some people here, but in ~10 years, I’ve never needed to write code for anything other than x86 or arm. So I agree with the author on their priorities.
Aside from various different variations of ARM, I’ve worked several variations of x86 and AMD64, SPARC, PowerPC, MIPS and others I’ve likely forgotten. Not to mention a few 8-bit CPUs too, but those there more than 20 years ago and not really fair to discuss here.