The logic is still flawed. The reason is that it's called spacetime, is that both the measure of the space and the measure of time dilate equally in a moving frame, so if the space were to appear to expand, so would the measure of time and the speed of light would remain CONSTANT!

Yet if intergalactic light is being redshifted, it is not Constant to intergalactic space. More lightyears, not expanded lightyears.

Two metrics of space are being derived from the same intergalactic light. One based on the speed and one based on the spectrum. Since the speed is still assumed to be the denominator, otherwise it would be a "tired light" theory, that makes it the base metric and so the spectrum has to be referring to distance and we are back to the problem this patch was intended to solve; The fact that as redshift appears to increase proportional to distance in all directions, it makes us appear to be at the exact center of this expansion.

Given we are at the center of our point of view, an optical effect would be logical.

While single spectrum light will only redshift due to recession, multispectrum light "packets" will redshift over distance, as the higher frequencies dissipate faster.

Though this would mean we are sampling a wave front, not seeing individual photons and that raises the question of whether photons, as quanta of light, are fundamental, or a function of measurement.

Which is too far outside of orthodoxy to consider, so we are supposed to accept Big Bang Theory and all its many patches and extrapolations.