Oh Jesus.

In classical redshift, when the train moves away down the railroad tracks, it doesn't stretch the tracks. The doppler effect is a consequence of the increasing distance.

The train tracks are the denominator, the distance is the numerator.

With this expanding universe theory, if there is a stable dimension of space, then the only way that redshift would increase proportional to distance in all directions is either we are at the exact center of this expansion and thus the entire universe, or redshift is an optical effect.

Since the only presumed optical effect would be the light being slowed by passing through a medium and the light was not otherwise distorted, it was assumed there was no medium to slow the light.

So then it was decided that space itself must be expanding, therefore every point in space would appear as the center.

Yet it still sticks with the classic doppler effect, that light taking longer to cross this expanding space is why it is redshifted. Yet that would make lightspeed the denominator. The metric defining the space.

As Einstein said, "Space is what you measure with a ruler." In this theory, the actual ruler being used is still lightspeed. That makes it the denominator.