I have been meaning to say something about this for a while now concerning Ignia claim of him and his fellow dragon gods becoming more powerful than Acnologia himself, while they were hiding from him.
here is why I don’t believe that it’s not out of the realm of possibility. First off, it’s beyond common at this point that the newer enemies being more powerful or at least being somewhat superior in someway to the old enemies. But also, it’s not anything new of someone hiding from an enemy that they can’t defeat at a certain moment in time and train themselves in someway to surpass that temporarily unbeatable enemy. Acnologia’s magic may have been unique compared to the other dragons and that he had to be defeated in a non-conventional way, that doesn’t mean that he just utterly can’t be surpassed by other dragons