By that logic, there’s also no such thing as a meter either. It’s defined as a distance light travels in a time interval proportional to the inverse of a frequency related to the caesium-133 atom. Definitions don’t mean there’s “no such thing” as something, it’s just a matter of if the units are useful in a given context. And meters are more useful in most everyday contexts.

Analysis is the fun part!

Probably relative to the CMB (the frame of reference where there is no redshift or blueshift bias in any direction).