Gravity as a force/phenomena in space on its own is actually very well understood. In fact it's possibly one of the most well understood theories we have in physics because of general relativity. However, at a particle scale we lack the understanding of how gravity would work.

Dark matter is the collective name for whatever "stuff" exists in the universe that we predict it should have, however because it is noninteractive in any way other than exerting a gravitational pull (it accounts for a lot of astrophysical observations that otherwise are bewildering given what we see in the universe). We know it should exist, we don't know what it is and can barely understand its current properties. So indeed, it is quite possible that it might be Aether-ish if we end up finding something else that explains our current observations or a drastic overhaul of how gravity works at large scales (the latter being very unlikely because of how well GR has stood up to experimentation so far).

With them, we can simultaneously explain lots of observed effects. But, as in the time of the aether, we know we don't have the whole story.