User blog comment:Zaiku K/The Next Dolls: Only Optimized for One Major Battle?/@comment-2037710-20140906031521/@comment-24419079-20140906153048

To be fair to Promestein, I concede that countering individual Heavenly Knights is a tremendous task, as I doubt any single creature in the entire trilogy (barring Ilias' final form) could stand up to all four at once. Even fighting two at once would be a stretch.

It is likely that other than Monster Lords, the Heavenly Knights are perhaps some of the strongest monsters since the Six Ancestors. Promestein herself said that the strength of those from the Great Monster Wars was much higher than the majority of the current generation angels and monsters (ie at the time Luka struggled against Giganto Weapon and it served as a prelude to the Heavenly Knights, but it was suggested to be vastly more powerful at its peak).