It makes things very different on Earth, too. Nothing really gets a lot of energy from absorbing a photon. Yes, there are a lot--11 million times--more photons to absorb, but you can't cancel one number with another one in this case.
Things look different than now. Everything then is pretty much one color, the "color" of a mirror. Every particle on Earth or in the sky that absorbs a photon re-emits almost exactly the same thing. Chlorophyll doesn't work. No photochemical reaction works the same as now. Plants starve. Eyes are blind, even though there are photons of the proper wavelength subspectrum to go around after all. The optical properties of everything on Earth are really screwed up.
You can't go there. But you already did.
Found a web page on Photon Absorption. There are three main processes of same.
µPE ~ Z5Where µ is an absorption coefficient.
µPP ~ Z2
µC ~ Z
Of those three, only the low-weighted Compton Effect seems to be momentum dependent. The other two absorb all the photon's energy and thus from what I can tell would not be so fragile in a Setterfieldian world.
A web page that ties at least some of the concepts involved together is here.
So cancel some of the alarm. ASSUMING I AT LAST HAVE THIS RIGHT (but I'm no physicist), we have the following.
Chlorophyll still works on Earth. So do eyes. However, we also have restored another factor of 11 million that the Sun has to swell, since opaque things then are indeed almost as opaque as now and they are getting all the photon energy, not just that tiny momentum. I hope it's clear by now that I don't think opacity does good things when it "works."
It also means all of the energy and not just the momentum of a given photon is available to knock gas particles across space. That means radiation pressure on free-space objects should have worked 11 million squared times better than now in the first days and in proportion with c squared down the decay curve. Given the alleged decay of c just within historical times, we should perhaps see things relating to dust clouds happening faster in the 170,000 light-years distant Magellanic Clouds than in closer objects like this one. The slowed-frame effect which has been invoked repeatedly on this thread is still there but shouldn't cancel.
Astronomers should be arguing over the odd "speed-up" effect as you look back across time in the dissipation of dust and gas around stars. I am not aware of such a discussion. This would seem to be a failed prediction.