Was Incursio really weaker than Grand Chariot, or was Wave just delusional?
Currently there is no actual way of knowing this, especially not in the anime variety as this bends off from the manga's story quite a bit.

Wave states that Incursio is the prototype of Grand Chariot, meaning it was created after Incursio. (ch 18, p 36) (ep 10)
Its full capabilities, however, have yet to be revealed and it is therefore unknown if it is more powerful than its predecessor, Incursio.

But assuming that Incursio's Adaptation &amp; Evolution are limitless, we can most likely state Incursio to be the stronger armor. But as we get to know in the manga (do not believe this is shown in the anime) it also has huge side-effects
spoiler from the manga

 However because Tatsumi forced Incursio to evolve rapidly to increase his strength, Incursio started to manifest in one of Tatsumi's eyes. After being examined by a doctor, he reveals that the armor has started to bond with him. He also states that after a few years Tatsumi could use it without overdoing it like Bulat. Now at the risk of being devoured by Incursio, Tatsumi can only transform 3-4 more times before Incursio consumes Tatsumi.