I don't get your God of Nen argument since the series already established that nen gets stronger when conditions are placed upon it. Remember Kurapica and his chain? He can only attack the Spiders and if he doesn't keep this condition he dies.
But who honors these contracts? The fact that by thinking 'this is my rule' and Nen accepts it gives off the vibe that Nen is a sentient force. I'm not saying this is the case, or that I support the idea. I'm just throwing that out there