I am afraid that you missed the point about the loss of light energy as the universe expands. True the omega was still one after annihilation, with most of the omega being in the form of light.
But as the universe expanded the total number of photons did not change. What did change is there frequency. General relativity maintains that the speed of light is constant for all time. As space expanded the wave of each photon also increased, so that its frequency dropped in proportion to the size of the universe. So the total energy, or the the omega due to light so decreased. The light omega decreased by a factor of 1,000 since recombination alone. It probable decreased even more before between annihilation and recombination recombination. No serious scientist today includes the omega due to primordial light as a significant contributor to the critical energy or mass.
I did not say that General Relativity was incorrect. What I did say is that calculations of the expansion of the universe based on General Relativity require an omega of one, at least until recently, for us to even be here. I think you probably agree with that.
What I am looking for is the missing that allows omega to be one even as the omega due to light was decreasing linearly with the expansion of the universe. I think you would agree that after annihilation, omega was primarily energy. Now from annihilation to recombination, mas and energy were still in equilibrium, so we can expect a equipartition of mass and energy in some sense.
After recombination, light was decoupled from matter, now in the form of neutrons and protons.
So for omega to be one from recombination to now, the omega due to light being released at recombination had to be insignificant.
So lets suppose that omega was one due entirely to mass or matter at the time of recombination. Most of that mass already had to be in the form of dark matter according to galactic cluster calculations. That means that dark matter, whatever it as, was already the dominant omega.
And light could be insignificant where omega is concerned.
But there is still an Omega problem from recombination to now, one that is close to the ideas of General Relativity. It has to do with the Cosmological Constant. The cosmological constant is another way to express the dark energy of the universe that astronomers now believe amounts to an omega of 2/3, whereas the dark matter is an omega of 1/3.
The problem is that the dark energy omega increases with the size of the universe. According to Guth the cosmological constant, which is based on the vacuum energy, is indeed a constant when expressed as a density. So as the universe expanded the total dark energy increased with its volume. So the dark energy omega increased by 10 to the 9th power since recombination.
So to summarize the omega problem, the dark matter omega decreased by a factor of three since recombination, the dark energy omega increased by 9 orders of magnitude since recombination, and is presumably about to blow the universe apart (in the next few billion years) if it keeps on going,
and the omega due to ordinary matter, which after annihilation should have been insignificant, has somehow increased to about 0.01.
So please tell me what the missing physics is that keeps Omega at one over billions of years. At this point it could be argued that we need an all-powerful god just to keep omega at one.