I dont champion anyone when it comes to cosmology. Most of the cosmos has not been explored. Einstein wrote GR with the working knowledge astronomers had in the late 1890.
He wrote GR with the belief that the Milky Way was the only galaxy in our cosmos. Furthermore, his limited knowledge encouraged him to present the universe as static.
It was Hubble in the 1930 that discovered the MW galaxy was not the only galaxy. In addition, Hubble showed that the universe was expanding.
Einsteins grasp of gravity only extends to the inner part of a galaxy.
What lies at the edge or outer edge of our galaxy GR could not explain. He supported dark matter, because it artificially extended the reach of GR beyond its intended grasp.
It would be interesting, to see the form if any GR would have taken had Einstein been privy to our current knowledge of the cosmos.

Let your curiosity change the model from spacetime to fluid like. Treat gravity as the result of space moving from a source to a sink. Let mass absorb space as the reason for the attraction between masses. If you can identify the source, you will see how DM can hold onto single galaxies.