This is where the politics will get even harder. So far we've been doing stuff that's unambiguously good and beneficial for everyone, but the next* phase is going to involve stuff that can benefit individual nations.
Well, I imagine it's much easier to use these to power effects in the nation than it is to project the power outside of the nation, so it might actually help keep the peace?
As long as people don't get clever and use it to create mass scale magic artifacts or super magic artifacts, I imagine this is the sort of power that's hard to directly use offensively against other nations. Indirectly, sure, increasing crop yield or even nutrition, destroying enemies in the nation, or buffing troops in the nation, would lead the nation to be individually stronger, but if we crack that sort of thing every involved nation would have a similar benefit and thus similarly grow stronger at roughly equivalent rates .... outside of the Dawi and the Eonir.
Which, shame for them, but I think the Dawi are confident enough in being able to trust the Empire that they won't mind, and the Eonir .... even if their rate of "grow stronger via more food/defeating invaders with less causalities" would be lower then other nations, I think they'd be confident they can boost their defensive capabilities enough to offset the other factions advanced growth.
Like, just off the top of my head, if they start gearing up a few years ahead of time, with all of their mages I think they could give their forces all a "see through fog" enchanted object pretty easily, set their nexus power to "permanent dense fog everywhere in their own territory" and be basically untouchable to invading armies as long as no one starts shutting off Waystones.
I'm not saying you're wrong, in fact I'm confident you're right, but I think it's going to be hard to use this sort of thing outside of a factions territory, and that fact is gonna be enough to get the various factions on board with this, even if begrudgingly.