Throughout Final Fantasy tradition, characters were either grand adventurers on an epic quest or freedom fighters. Final Fantasy XV joined both traditions together. And as a model, I’m sure they used Final Fantasy V & VI for this dichotomy.
The former is a grand adventure and the emphasis on Final Fantasy V, before it became about Ex-Death, was exploring. Bartz and his harem went around the world investigating the damage of the crystals and fought summons along the way. When it did become about Ex-Death, characters needed the legendary 12 weapons (instead of 13).
Much like Noctis gathered armigers in Final Fantasy XV.
The latter is a fight the empire story with a much clearer bait-and-switch for the villain. Summons play a bigger role here than they do in Final Fantasy XV (and that they ever had previously). When Final Fantasy VI raises the stakes, it splits the world into two (World of Balance vs Ruin).
Both Final Fantasy V & VI were benchmarks of their time. Final Fantasy V was more so a perfection on the old school tradition. Final Fantasy VI was a leap forward into the possibilities. Final Fantasy XV incorporated both these groundbreaking elements and is why Final Fantasy XV feels like two separate games.