So far as FFXIV is concerned, Omega is certainly very powerful. Excluding the WOL, who kills literal gods as a warmup to bench pressing ascians, Omega was believed to be the reason Nael brought Dalamud to Eorzea, not just to scorched earth policy Cartenau in the literal sense of the word, but because Omega was the only thing Garlemald knew about that could not only reasonably threaten them, but could very feasibly level entire sections of Garlemald overnight. Omega's also very explicitly geared to fight dragons, the thing that Garlemald has historically been very, very bad at.

All that said, I wouldn't come anywhere close to saying they're the most powerful. Keeping in mind:

- Ascians are essentially gods unto themselves. Emet-Selch (<- Shadowbringers spoilers), Elidibus, especially when augmented with the Crystal Tower(<- Even more Shadowbringers spoilers), and Venat

(<- Endwalker Spoilers)