Large objects and small objects will orbit at the same rate as long as they are at the same distance. This is the same principle demonstrated by Galileo that objects accelerate at the same rate. Orbiting is basically falling if just takes longer. Now there is some difference in rate because relativity and all but the difference between the postulated little objects and big objects is not enough. Unless one of the big objects is a planet. So they almost would have to say that planets aren’t planets to make the theory work.
“and all but the difference between the postulated little objects and big objects is not enough. “
I think the article says that lots of little objects have the same influence as one big object.
Major problem is that galaxies ignore that law. After reaching about two thirds of the radius out everything orbits at the same rate regardless of mass. To account for that big problem, Cosmologists invented magical unseen things composed of undetectable but somehow massive dark matter. . . which to this day they still can’t find, no matter where they look.