I reread your essay.
It is interesting to consider what is the strength of the relativity compared with the Poincaré theory, or Umov theory (I don't know this interesting story): what is the characteristic that help the human revolution? I think that your reasoning is right: the strength of the revolution is in the world of ideas because we have not maps (mathematical description) of the physic frontier.
I think that the abstract mathematical construct like wave function (visible interference fringe) and four dimensional coordinate (perihelion precession of Mercury) have a direct observable measure but I think that your idea is more deep: I understand that now, in this age, we use a construct that must change in some thousand years (in an other mathematical frame), with a simpler description that is true like this (if it is so, that is interesting).
When you say that the laws of Nature exist independently from the coordinate system, then you say an interesting thing (that I don't notice in the first reading): the laws are true for each system, considering all the transformation, and apparent forces.
I have ever used a different synchronization, using the reflections time along AB, then I must to make some calculation to verify all (I understand that in  c+Uab is an approximation, because the velocity cannot be greater of c).
I voted your essay some day ago, like all the other, but I make a quickly read: each essay merit a reading for the innovative idea, but my vote are not ever generous.