Ok, 36 relative units does feel excessive. Reading each of the names, I can understand why many were added. Still, that is a lot and I can't imagine there are more than a handful of folks that can correctly use most of them. I'd also wager that the odd interactions that you are certain to get with them has to be a nightmare on large teams.
For implementors it is probably a lot (while it's trivial math usually once resolution etc. is known)
But for users:
> a handful of folks that can correctly use most of them
That doesn't really matter. For most developers a simple guide is enough, the ones with special needs have to know. They don't have to know all either, but different folks with different subsets.
Everybody else just has to know "there is more" and read up if they encounter something special.
outside of Q, I think I've used most all of these in one way or another for various reasons. Most can be done with calc() and whatever the nearest root value is - but some of them are handy, even if they don't appear so.
Again, going on the name, I can see easy justifications for most of them. I, sadly, can also imagine the rabbit hole that is justifying any particular one for a document. :(
