FYI, I’ve seen this kind of averaging typically done using iterative contour maps for daylighting, i.e:
If you made a histogram of each point in the grid (i.e. you sort and “bin” the points according to some constant interval of daylight factor), then each “bin” in the histogram would represent a contour. Cumulatively adding bins in reverse would then represent decreasing your average daylight factor by expanding it spatially from your brightest points.
Anyway, if you do end up going the histogram direction Mostapha, I just wanted to mention there is a histogram module in Ladybug.