"Yet" in present time, after VP managed to power the Mother Flame.
38 years ago IMU didn't have the means to completely eradicate an entire island.
I've already replied to your permanent peace. Harald's own foundation for it is wrong, because he is not accounting for the giants who don't want peace and diplomacy and who want to be warriors, not necessarily pillaging pirates, like his own son. Rebuilding Elbaf without them in mind is bound to backfire one way or another.
Again, for me, little armchair reader who has all the pieces of intel, the best course of action would've been for Harald to do deals with human nations in exchange for protection. They're afraid of giant scourges? Well, here's the solution: those giant scourges will now protect you from anything else around. And in the meantime, let our people mingle, let us show you that we aren't monsters, but that we have a rich culture, too.
It worked for WB. It could've worked for Harald. All he had to do is not reject his heritage so thoroughly, but use his people's might for peace.
Even if he thought the WG was the only solution, Xebec had given Harald more than enough information to make him realize that it's not tenable, that the WG are backstabbing rats who revel in genocidal games.
How's that for transcendent peace, Lee? The giantkin gets to be a part of the WG, as long as it partakes in the WG's crimes. Nice future Elbaf would have then.