But these are just contingent facts about experimental design. Consider an idealized experiment where one photon pair is sent out every hour by a source which is exactly at the midpoint between two polarizers, which catch every single photon with perfect accuracy. In that case all each experimenter has as far as data goes is a list of yes or no answers as to whether the photon went through the polarizer or not. There are no time stamps, distance measurements, coincidence intervals, or anything like that.
No, in the Bell test setup I described above, the basic datum is whether the experimenter sees a photon go through the polarizer or not. I think the word "correlation" is a much better term for what you call the "rate of coincidental detection". It is just the correlation between individual polarization measurements of photons, and as such all its properties are determined by whatever determines the results of individual polarization measurements. And the nonlinear relationship between the correlation and the angle is also entirely determined by whatever determines whether a photon goes through a polarizer or not.
All a local determinist might infer from this is that the decision of whether to go through the polarizer or not is based on some local hidden variable, but we human beings don't know the value of this variable, so to us it seems like an unpredictable 50-50 chance whether it will go through.
But the argument is not based on the known data from practical experiments done so far; if you wanted to respond to Bell's theorem in that way you could be like zonde, who believes that Bell tests to date have experimental loopholes, and that quantum mechanics will be disproved as soon as we improve our experimental capabilities. The argument I'm making is more fundamental: it is that it is impossible for a local determinist to believe that all the experimental predictions of quantum mechanics are correct, without regard to the practical difficulties of testing these predictions. It took us a while to do any Bell tests at all, but that did not change the validity of Bell's theorem.