I'm not proposing a theory. I am making an observation. Like pointing out the earth is not the center of the solar system is an observation, not a theory.

I am simply pointing out the expanding space theory is still premised on this expansion being in relation to the speed of light.

That makes light speed the denominator.

How would we know it's expanding, if we don't have some metric against which to judge this increasing volume?

Now if I was to propose a theory, it would be some other way of explaining redshift, than recession of the source, aka, doppler shift.