We know that spacetime is einsteinian, not euclidean, yes. But that's not what's being discussed here. The issue is whether the force of gravity deviates from the expected 1/r^2 value. Experiments, measurements and observations within the solar system have not revealed any deviation. The precession of mercury is not due to a deviation from 1/r^2; it is due to space near the sun being bent instead of flat. Ditto GPS; we have to adjust for time dilation and curved space, but not for any deviation from 1/r^2. MOND theories predict that MOND gravity is indistinguishable from normal at short ranges less than several light years; the MOND effects only show up at distances of many light years.
That’s kinda the whole point, isn’t it? I’m just a layman, but my understanding is that the incompatibilities of GR and QM point to a need for a proper theory of gravity. Looking at the dark matter problem from a purely GR-perspective will miss that context.
