Keep in mind the foundational axiom of General Relativity is the speed of light as a constant.

Essentially that in a moving frame, both distance and duration dilate equally, so space is always measured as the same speed.

Yet in this theory, of the expanding space, the speed of light does not increase, as space expands. It is assumed to travel at some stable rate and only the spectrum of this light is stretched by the expansion. Sort of like marking inches on a rubber band, then stretching it.

So two metrics of space are being derived from different aspects of the same light. One based on the speed and one based on the spectrum.

So which is the numerator and which is the denominator?

Consider that in basic doppler effect, the train moving down the tracks doesn't stretch the tracks, it only increases the distance along them. So the tracks are the denominator and the distance is the numerator.

In this theory, if the speed was the numerator, then it would be some form of "tired light" theory, but as an "expanding space" theory, the speed is still the implicit denominator. The metric against which this expansion is occurring.

So, in simple, mathematical terms, it makes no sense.

That why cosmology keeps needing these enormous patches; Inflation, Dark Matter, Dark Energy.

It's the current version of a geocentric cosmology and the epicycles to explain it. Remember epicycles were quite good math, because it modeled the fact the earth is the center point of our view of the cosmos, but the crystalline spheres proposed to explain it were flawed physics.