One problem with the expanding universe model is that it uses the premise of spacetime to argue that space expands, but ignores that would mean the speed of light would have to increase, in order to remain CONSTANT!

Instead, two metrics are being derived from the same light. One based on the speed and one based on the spectrum. Given that if the speed were the numerator, it would be a "tired light" theory, but as an "expanding space" theory, the speed is still the implicit denominator. The metric against which this expansion is calibrated.

With doppler effect, the train moving down the tracks doesn't stretch the tracks, only increases the distance. In this theory, light speed is still the tracks.

To be valid, a theory has to be somewhat coherent, which this is not. Given it can't be falsified, only patched with ever more extreme additions, Inflation, Dark Matter, Dark energy, it's not even science.

It's a belief system, in which the central premise cannot be questioned.

As for alternative models, it has been noted that multi spectrum light "packets" do redshift over distance, as the higher frequencies dissipate faster, but that would mean we are sampling a wave front, not seeing individual photons having traveled billions of lightyears......