I think you misunderstood my post. My parent post argued that a mass-proportional charge imbalance big enough to cause a measurable change in gravitation would

I think you misunderstood my post. My parent post argued that a mass-proportional charge imbalance big enough to cause a measurable change in gravitation would have catastrophic consequences for planets. Indeed, this is not true, the effects on the planet are of the same scale, i.e. ridiculously small. Of course, as I wrote, both laws follow the same power-law, so this can not solve the dark matter problem. Indeed you can absorb it in the gravitational constant. I also did not suggest that electromagnetism should be different at the scale of solar systems. A test of the charge equivalence of protons and electrons to 8 digits is by far not good enough to rule this out. You have to probe the proton charge to ~1E-20 for a 1% change of the gravitational effect. This is beyond the reach even for atomic level measurements. More interesting are the bounds on charge conservation.