I'd have to say hauling 10 dead-weight Paragons with 5 combat ones is probably the surest way to take on 3 or more full Ordo fleets at once. The 15 minutes of 100% combat readiness is where it's at. Not to mention unlimited ammo and health. Could get 3 fleets down in about 7 to 10 minutes.
Idk I haven't tried Onslaughts yet, I suspect their armor tank would fail eventually though. I have a feeling that they might be more powerful because each Onslaught has as many ordnance points as a Paragon.
The legions were a challenge build and I honestly didn't think they would do that well. I only got them to work by working with their burn drive ability. Kill everything as fast as possible. Hard to balance flux with such terrible flux stats on them. They can only take on two fleets at most because they will run out of Harpoons.