Or we might just have some epicycles type situation, where any of the initial premises are mistaken and the anomalies have to constantly patched with ever more fantasical additions.

So are there any gaps too big to patch, that have to simply be ignored?

Consider that before Inflation, Dark Matter and Dark Energy, the first big patch was when they realized that as redshift increases proportional to distance in all directions, it makes us appear to be at the center of the universe. So the idea was changed from an expansion in space, to an expansion of space, because "spacetime!"

Which totally ignores the central premise of SR, that the speed of light is constant to its frame.

If intergalactic light is being redshifted, it is not constant to intergalactic space. More lightyears, not expanded lightyears.

This notion of expansion still assumes a stable metric, against which this expansion is measured. That makes the speed of light the real ruler.

Though raise this particular argument in polite company and it will be ignored, not answered, because the answer isn't there.