Webp adoption also used to terrible, but now it's mostly fine.

Yeah, I guess if we're being pragmatic/reasonable, you are right. I think jxl use and general adoption would be much more of a symbolic win than a technical one. The problem is that a new image format only reaches general adoption if Google supports it. Webp is a decent Google-developed standard that has reached general adoption because Google pushed and supported it and if Google doesn't support jxl, then you can't use it on the general internet.

This is not about jxl being the better standard, this is about the better standard being non-viable because Google doesn't want it to be.

The caveat here is that jxl is not half as old as webp and this situation might change drastically in a matter of months (I bet ff would be quick to adopt jxl if Google did...) ((although the jxl standard is technically 3 years older than the webp standard))