This language seems to completely overlook the reality of what models are in physics. We just don't make claims on reality when we make models, we make claims on the models (that they adequately describe the current observations of reality).
I'm making a claim on reality when I make my models. They might turn out to be incorrect claims, but they are claims nevertheless.
We have no idea if a photon is massless, if c is constant, if dark energy is constant, if the universe is infinite, if curvature is zero. That's not the point at all.
That's exactly the point.
We have experimental data that puts tolerances on those values. We then make physical theories that make statements about reality. Electroweak theory says that the photon is massless. Relativity says that c is constant. It could very well be that the standard model of cosmology in 2020 says that curvature is exactly zero.
Those are claims. If it turns out that the photon has mass, then electroweak theory is wrong. The standard electroweak theory in 1974 stated that the neutrino had zero mass. That turns out to be wrong. The standard cosmological model in 1995 stated that the cosmological constant was zero. That's also wrong. We make progress by making claims, and if those claims turn out to be false, then GREAT!!!!
The point is to ask, can we adequately understand our current knowledge of reality using a model that uses massless photons, constant c, constant dark energy, and an infinite universe with zero curvature.
The point of a theory is to go *beyond* current knowledge. Once you claim that the neutrino has zero mass, you can calculate the solar neutrino flux, and then you find that it's not what you think it was.
And for the data we now have, the answer to that question is, "yes."
It's actually no. There are lots of things about the universe that don't make sense. LCDM falls apart once you start calculating power spectrum at galactic scales. Also, there's always a lot of noise in observations.
But we have no idea which in that list will be the source of the "no", all we have, all we ever had, have, or will have, is the current best model.
And any model is afraid to be wrong isn't very good.