The following isn't exactly an "answer", but an opinion or an interesting hypothesis to be debated (at least from my own view point !).
It feels very "natural" to me that the cosmological fluid of "dust" matter should be under tension (i.e. should produce some negative pressure), a bit like some kind of Van der Walls gas, or a kind of polymer fluid. At very long range, a given particle doesn't produces any noticeable global attraction on the whole. But at close range, it certainly creates some attraction on its surrounding (i.e. on a few other close particles). So the gas particles has some close range interaction, that is not described by the standard "dust" equation of state ($p = 0$).
In the standard FLRW cosmology, it is already assumed from the start that spacetime has exact local isotropy and homogeneity, while matter doesn't respect that symetry principle in reality (the symetry is only "statistical", on a very large scale). It always striked me that cosmological mega-structures (galactic superclusters, "matter bridges", cosmic filaments, ...) are looking like some stretched material that is under tension. So it's natural to ask if the "dust" gas of galaxies is really well described by the equation of state $p = 0$. I now seriously think this is actually a very bad idealisation, and it's not a surprise to me that we now see some weird cosmological effects like "repulsion", "dark matter", etc. We may be applying and interpreting general relativity in a very wrong way !
It is well known that the Einstein field equation is highly non-linear and may show some subtle "back reaction" effects from the sub-levels on the higher levels. The importance of "back reactions" in general relativity is very much debated today, and there is still no clear agreements on it yet. There's a LOT of litterature on that subject, while is it not well known enough in the scientific community (AFAIK).
I personally highly suspect that general relativity is trying to tell us something very important about gravity : it is hierarchical (the Einstein' equation is not scale invariant). Gravity may act differently at different scales.
So when we transpose the $p = 0$ dust gas (that comes from the small human scale) to the much larger scale of a fluid of galaxies, we may actually do a very huge mistake !
It's possible that, because of the exact symetry requirement, the standard RWFL cosmology is simply neglecting the galactic interactions in the "dust" gas (i.e. the small scale short range interactions between the particles).
I think that we cannot transpose (from the human scale again) the usual dust equation of state to the cosmological fluid. The rules are not the same at the large scale.