Thanks to Vera Rubin's observation of 1/r velocity dependence of spiral galaxies, we already know that something is seriously wrong with GR. Fully 1/3 of the stars in the outermost portions of spiral galaxies have already achieved escape velocity under GR, yet they are not escaping. Dark energy was devised to account for this discrepancy. Space in the vicinity of a gravitational field can have inertia too, if you consider the mechanism by which the SM proposes it gets it. Whatever the boson(s) involved, one cannot give gravitational inertia in linear or spin forces to matter without the bosons creating that force getting gravitational inertia back themselves, by Newton's third law. If the bosons are in free space, then space gets that inertia. Unless you believe that gravity is some form of reactionless thruster or perpetual motion machine, that is. That sort of idea used to be frowned upon, once upon a time. At least, Dark Matter is an improvement over either of those.