But that doesn't address the point that JPEG XL is only marginally better and has a gigantic mountain to climb if it ever hopes to displace JPEG (and likely never will given the vast set of JPEG files that exist and will never be converted).
And not only that, it's reasonably fast to encode on consumer hardware.
JPEG XL has the ambition to supplant all the images formats of the next 20+years.
You will have to define what is marginally better. WebP is definitely marginally better than JPEG. And JPEG XL is easily 30- 40% BD-Rate at the same quality at BPP 0.8 or over.