That does not mean that he is right. But he is certainly right that the various theories of gravity, namely GR in which gravity does not exist, and all the rest which postulate a more or less Newtonian gravity on a flat spacetime, are fundamentally in disagreement.
I have only skimmed the link. But it seems to be arguing coherently. I missed the point about dark matter. But the main point about the speed of gravity has to be correct if black holes are to exist.
It is the huge mass within the event horizon of a black hole that sucks up matter, (and space as well if GR is correct). The event horizon is where photons are trapped because either gravity prevents their escape (flatspace) or space is sucked in at the speed of light (GR). However, gravity, if in particulate form, must travel at even higher speeds, perhaps 10^10 as he suggests, in order for the mass outside the event horizon to feel the pull of gravity from the mass within the event horizon.
Some physicists hand wave this by saying that the gravity particles are virtual, and virtual particles can travel faster than the speed of light. Without a theory of gravitons, this is only hand waving.
I prefer the evanescent wave approach. It has been shown experimentally, that for the case of the propagation of light, that in a medium where absorption dominates so that the wave becomes exponential, that the propagation of the exponential wave is instantaneous as far as anyone has been able to determine. Sorry but I do not have a link for this. The experiments have been done in the last 2 or 3 years.
So static electric and magnetic fields are also evanescent or virtual if you wish. It follows logically, but you can never completely trust logic, that static gravitational fields behave like virtual particles or evanescent waves and propagate almost instantly.
Not sure how this negates dark matter. I'll read more carefully and respond later.