You're making a guess without much physical basis. Number two, a galaxy is not equal to a galaxy. They differ in size and luminosity. They bump into each other and merge. What we discovered . . . is that the velocities at which the galaxies move are not the same velocities at which the particles move.
Galaxies are somewhat slower than the particles.
You can't see that unless a galaxy is made up of several particles. Confident of the simulations' accuracy, Zurek's group returned to calibrate Davis and Peebles' methods by treating the simulations as if they were observational data. Davis and Peebles compensated for this and other effects using a special procedure. An untreated look at their sample and other surveys resulted in the same figure as the simulations. Either this dark matter exists in the universe, or we know nothing about gravity.