[jamesmaniscalco]

If "time slows down over time" then we would still observe the light at its original frequency - why would the energies of the states of hydrogen atoms in distant stars change over time, but the energies of the photons emitted long ago not change?

How does this hypothesis account for the CMB?

Wikipedia has a nice summary of alternative cosmological theories (and why they are often dismissed by experts):

https://en.wikipedia.org/wiki/Non-standard_cosmology#Proposa...