I am not going to start into a line by line argument, when it appears from the start that you are fixated on your own bias. There are a couple, of what I see as errors in your position, that I will point out.
You seem to see or consider singularities as a fundamental component of GR...
When Einstein presented GR he was presenting a field description of gravity, beginning with SR and based on observations of the solar system, initially extending the implications to a prediction associated with the gravitational deflection of light. No singularities! This is a place where re-reading the rpenner quote in my earlier post would serve you well.., if you can set aside your preconceptions long enough to understand how it impacts the discussion here.
The concept of singularities came later as others applied his (Einstein's) field equations to extremes involving strong gravity.., which could only be arrived at by making assumptions about the fundamental origin of gravitation... Even though GR is a field description of the mechanics only, not the why or how. It is almost as if someone was having trouble setting aside the Newtonian assumption that gravitation was an attractive force.
However, the real point is that GR did not begin as a field description of a galaxy, the universe, or singularities. It began as a description of the gravitational field of our solar system. Within that context it has been a successful description and testable within reasonable limits... And so far it has passed those tests, which makes it an accurate field description of the gravitational dynamics of the solar system. Beyond that we speculate... And we sometimes have to incorporate things like dark matter and dark energy to keep the model in balance with what we observe....
... It is not just that within the context of this discussion SR and GR are approximations, all theories are at best approximations. And they will all remain approximation until we arrive at a true fundamental understanding of the how and why. Even then the big picture will likely be far too complex to do more than approximate how, the how and why results in all that we observe when we poke reality.
.... I am one of those who believe, note I did not say know.., that the equivalence principle is more than an approximation or some kind of happy coincidence. I'd even go as far as to say that over the last ten years or so, I have begun to believe that inertia and gravitation may be two sides of the same coin so to speak, which would explain the equivalence principle, as representing more than just a chance similarity.
