Razrah (Leanon)
I agree, the OP fights should be limited to GvG only and furthermore: 6 OP limit per guild is too high, 2 are more than sufficient.
Well, suppose there are enough homins/guilds on Atys.
Anyway, just to mention it. In the past on Leanon a couple of guild members left their guild just to join another for a fight and after the fight they just jumped back into the other guild. Reason for this in the past: alliances and such...
Thus there is a way around, but fundamentally the idea is good.
Raz from Exeter ^^
Can be prevented by setting a long limit to who can join in the fight as attacker. Say 3 weeks for the attacker and only the attacker.
That way attacker can't swell their ranks with temporary members from other guilds, leaving the defenders with no way to defend themselves as they can bring in such mercenaries.