Fred,

"But relativity is a thing, not dependent on big bang, the doppler shift you hear in the siren of a fast moving emergency vehicle whizzing past is relativity at work."

With Doppler shift, it is the distance, measured in an otherwise stable dimension of space, that is increasing/decreasing.

When they realized that redshift increases proportional to distance in all directions, making us appear to be at the center, the argument became that space itself must be expanding. Which directly contradicts Relativity, given that if relativistic space were to expand, the speed of light would have to increase, in order to remain constant.

As it is, two metrics are being derived from the same intergalactic light. One based on the speed and the other based on the spectrum. If the speed was being treated as the numerator, then it would be a "tired light" theory, but since it is an "expanding space" theory, the speed is still assumed to be the stable metric, against which this expansion presumes to occur.

As Einstein said, space is what you measure with a ruler and the ruler in this theory is still the speed of light.

Wonderful as it is, it should not take a ten billion dollar telescope to realize it's bad grade school math.