Can you provide a source? We've seen Thor interfere with the world directly, the thunderclap over Cliffport comes to mind, as does the storm on the airship.
Yes, hence why I said "if you're willing to take that passage as truth". I'm skeptical of quite a few things in there.
I think we're getting tripped up on verbs here. You're saying that the Twelve won't sink Gobbotopia, and I agree with you. But I'm saying that they could. And if you're Redcloak, are negotiating concessions from those gods, and have very little faith in those gods to value the lives of the goblinoid citizens of Gobbotopia, then you'd probably want it in writing that they won't.
And if you're the Twelve Gods, you don't want the Northern Pantheon giving away parts of your territory to other people. It's the Northern Pantheon making the concessions, why don't they give some of their territory?
I'm not making any predictions about what's actually going to happen to Gobbotopia/Azure City, I'm just trying to look at this negotiation from the perspective of the involved parties, and seeing an incoming problem. And obviously this problem can be solved in a manner of ways, like the other two pantheons agreeing to give as much territory as the southern ones do, for an obvious example, but it's still going to be a problem that needs solving.
As a reminder, the perdiction and argument I'm making here is that this negotiation won't go south from the intervention of Xykon, Roy or some other third party. I expect the deal to become a lot more difficult before anyone comes to an agreement.
I'm more reading it as a political issue. Any god could intervene anywhere, but if they have disagreements that could create a god-killing snarl, so they agreed to give each other their own space where they're always right. The problem with the Dark One is that he's definitely a god, so he has to be allowed to do his god things, but all the gods would prefer that he do it somewhere else than on their territory.
EDIT: Gotta go for now, I'll have to catch up on this discussion later!