What about when everyone assumes the blunder to be fact and so they keep adding patches and excuses when observations don't meet predictions, like our current cosmological model?

Before Inflation, Dark Matter and Dark Energy, the original patch was when they realized that cosmic redshift increases proportional to distance, creating the impression we are at the center of this expansion, so it was changed from an expansion in space, to an expansion of space, because "spacetime!"Which totally ignores the central premise of Relativity, that the speed of light is always measured as a constant. If intergalactic light is being redshifted, it is obviously not constant to intergalactic space.

The Doppler effect is due to a changing amount of distance between source and observer. The train moving down the the tracks doesn't cause the tracks to be stretched. Similarly, if these galaxies are moving away, it doesn't stretch lightspeed. There are presumably more lightyears, not stretched lightyears.The speed of light remains the real metric/ruler, even in ths theory.

We do happpen to be the center of our point of view, so an optical effect would be worth considering and multispectrum light "packets" do redshift over distance, as the higher frequencies dissipate faster, yet that would mean we are sampling a wave front, not observing individual photons, which would throw a real monkey wrench into the presumed fundamental discreteness of photons.