In the middle of galaxies are black holes. If the mass of those black holes is greater than previously thought, then that would explain why these galaxies are assembling more quickly. It also may solve the problem of the missing mass needed for the universe to undergo the Big Bang. But this is just conjecture on my part.
P.S. I hate dark matter theory.
There is variability in the speed of accretion.
Given that difference and the variability of galactic matter distance and density, there is no constant rate of black hole formation.