Historically, even when the "real" druids were at the zenith of their "power", warlords, chieftains and/or kings still held much control (=law) over their people, and a case could easily be made that it was closer to zero than 50%. Translating based on a fantasy interpretation of this historical perspective, their greatest areas of effect IMO would be 1) Temple and (in RoE game play), #2 could be Source (which could be 100% or 50%, depending on what you are trying to accomplish). I think the real For game play, 50% for Law seems plenty to me, but as stated earlier, if you go full temple, full source, half law, Druids are/would be the only class that gets/would get 2 full and 1 half. All others add up to 2, excepts wizards and sorcerers who get 1.5, and from a game balance perspective this should also be considered, if not evened out here, then perhaps in other areas (as suggested on another thread).
