I love APCA, Myndex (Andrew Somers, APCA author) was an absolute inspiration to me for getting interested in color, I wouldn't have known 1% of what I do or have done 1% of it without his deep dives showing how to work in this space.
It has an interesting effect on the community in that the general language around it is read too strongly: it is an important and crucial advance, getting science-backed data on exactly the right contrast in multiple scenarios is _absurdly important_ in a world of Ambient Computing™.
The mistake that's made is reading into this too heavily as _the previous spec or WCAG aren't based on data at all_.
Yes, the calculation is based on absurd stuff -- 100 nit monitor, you can't track down a source for every bit of it.
But there's a _whole separate field_ that spatial frequency comes from and it is _very_ well known and understood.
Most importantly: the APCA predictions for contrast were only about 5-7 L* different last time I checked. This is important, thats a _lot_ --- but it also isn't a lot, that's on a scale of 100. What we have today isn't completely utterly alienly different and broken.
Comparing the difference in T will be enough as long as the luminance measure APCA relies on is monotonic to RGB (HSL's lightness is hilarious, its the max of RGB minus min of RGB)
On the same topic, any thoughts on https://www.myndex.com/APCA/ and approaches if this becomes a standard? It looks like it complicates color palette design and the contrast depends on which color is the foreground and which is the background.