Wave states with great confidence that Incursio is weaker than Grand Chariot, because Incursio was a prototype for Grand Chariot, etc.
The early clashes between Wave and Tatsumi can lead the viewer to such conclusion, but Incursio's has the ability to evolve (from the beast it was made of), while Grand Chariot doesn't.
If you watched to the finale, we can see that
Tatsumi causes Incursio to evolve so much during the fight against Shikoutazer that it even gains the ability to fly. While it is enough to defeat the emperor, unfortunately not enough to save Tatsumi's life.
Considering this, I don't think that Incursio was the weaker one. Is it so?