> ... Linux boot time is so much shorter than whatever the BIOS does before it hands control over
On which system? Is your machine, for whatever reason, re-doing "memory training" everytime it boots? This is one can be really slow.
Who knows, but any desktop and laptop I had access to in the last decade spent more time in POST or whatever than it does in OpenRC. Might be more of a case of the Linux bootup with a minimal set of services I actually need already being pretty fast even without paralellism rather than those BIOS being particularly slow. Windows for example is a lot slower there from my experience - and the difference is even more ridiculous for shutdown.