Factions are currently ranked by total rep. Rep means nothing. Anyone can build up rep at low level teams then not be raided as their team level rises so rep never really falls again. I have had some shockinglyninactive players with misleadingly high reps. You can also have factions sitting on high level rep players who haven’t logged in for months. Rep really does mean nothing.
League placings do give some idea of activity, but what about if the faction info also showed where the faction placed in the last faction up events? So if it showed recent history for the last war, raid and survival road tournament? That would be a better indication of how good a faction actually was.