Note that fighting a Third Circle is still on the level of fighting an overwhelmingly powerful god-being who can fuck up your shit unless you have perfect defenses. Remember that Ligier alone can be summoned and pull out his sword and throw it into the air and the sword alone will fight off entire armies and any challenges and then, if you manage to defeat just the sword, he will then gracefully concede the fight rather than going all-out with the city-shattering nuclear hellfire.
It’s easy to forget that while Malfeas is a Dyson Sphere, Ligier is a sun.
And yes, he is an acceptable final boss.
So while Jon has a point, its less of one than he thinks it is. Third Circles include stuff like a ravine that is literally infinitely deep or a being of millions of eyes whose sweat drops to the world and forms buildings made of glass. If Yozi are the map, it’s the campaign map and the individual Third Circles are themselves entire dungeons.