I have been studying how to do cosmology with inertial coordinates, not the Friedmann coordinates that cause such dogmatic chaos.
For instance, kinetics in an inertial frame show extra supernovae Ia dimming with distance as evidence for slowing of expansion if anything. The departures from the expected dimming are 10%, and could have other causes. The Friedmann coordinates are noninertial to the point of changing the sign of the usual unwary calculation! Things not having a magic velocity are said to have cosmological acceleration by measure of Friedmann coordinates; the light signals from supernovae are included in this fictitious effect.
It is proclaimed that the typical distance scale of variation, from peak to valley, of the temperature in cosmic microwave background proves the flatness of space. But flatness within the Friedmann coordinates does not imply flatness in inertial coordinates. A flat and empty universe by inertial standards would possess negative curved space by measure of Friedmann coordinates.
This typical distance for variation in the background is extrapolated to a present size of 206 million light years, when an inertial or geodesic version of space is used. So, if this is also the typical spacing between superclusters and the middle of the adjacent voids, then space is indeed flat. But flatness in Friedmann coordinates implies positive spacial curvature in inertial. The positive curvature would magnify the variations in the cosmic background. And acceleration or deceleration trumps curvature with a stronger effect. So, if the spacing of superclusters is smaller today, then both counts imply deceleration of the universe.
Michael J. Burns