THe most active groups, are those that trade a lot. Or in the case of the [AI] at the moment a group that mixes trading with armed action, fighting corsairs and alike. GRN is dead, I barely ever see a GRN on. I see a fair amount of RNS around, so its not like that house would with out representation if GRN lost its officialness.
But there are serious problems it seems with house miliateries. I think perhaps one major problem is the way these groups fight. If someone is getting shot at and communicates in the Emergency channel, some one who on that day did not feel like playing FL may feel that they HAVE to come in and do something. Compultion of that kind makes the game more like a chore. Though in fairness I can't think of an alternative. I would have no objection to reinstating consequences for lack of activity, because not only does it damage your own faction it has repercussions for other groups.
If your faction's main/only enemies never log is there anypoint, and Groups like GRN are the enemies of a lot of factions.