I thought that was actually true. Why are you calling it tired and old?
Because there is no reason to expect stars going around a galaxy to follow keplers laws for two body systems. I have yet to see the measured rotation curves compared to an "expected" curve where the author doesn't use Kepler as part of the expectation.
Just a year or two ago, I saw a paper in Nature where they were looking at a gas cloud forming a star, and they compared its rotation to something based on Kepler. I just had to shake my head - the correlation was there but not a great fit of course. The curve is interesting, the comparison not so much.
The 'Kepler' law for galaxies are modified to accommodate for a mass distribution. See e.g.: https://en.wikipedia.org/wiki/Galaxy_rotation_curve#Halo_den...
This profile closely matches the expectations of a singular isothermal sphere profile where....
Why should the dark matter form a spherical blob? Right, because that's what makes Kepler behave better. But how the heck does the dark matter behave? Why should it take this distribution? It seems to be all made up to only explain observation, but not itself.