Cause : A reduction in the decompression of space* over distance (due to the presence of mass).
Mainstream theory: Photons are emitted in a region of higher gravity with Energy A, and received in a region of lower gravity with Energy A, where Energy A is lower than the Energy B that would have been emitted by a similar event in a region of lower gravity.
Evidence: There is plenty of experimental evidence to support this theory.
Cause: A reduction in the decompression of space* over time (due to universal expansion).
Mainstream Theory: Photons were emitted in the distant past with Energy B and received in the present with lower Energy A, where B is the energy that would be emitted from a similar event in the present.
Evidence: No hard evidence that I am aware of. Some may argue that CMB was emitted as ultraviolet radiation and we now see it as microwave radiation. I agree, but if we are being consistent with the hard evidence we have about gravitational redshift, then we should expect that time is moving much more quickly today than it was when the CMB was emitted, just as it moves more quicky in regions of lower gravity. So yesterday's ultraviolet wave is today's microwave - with the same energy.
*I use the word space for brevity, but really mean the universal metric through which light travels.
As far as I can see, apart from their causes, the only difference between cosmological redshift and gravitational redshift is that one happens over space and the other happens over time. So why is the mainstream view on cosmological redshift inconsistent with the mainstream view on gravitational redshift, for which there is ample supporting evidence?