If Louisoix hadn't been at Cartenau, we probably would be looking at the destruction of all of Aldenard and Vylbrind at a minimum. No Louisoix means no Phoneix which means Bahamut never dissipates at Cartenau. Who knows what Bahamut would have done once he was finished trashing Cartenau? Well, maybe it's not quite so much of a mystery. We know he and Sophia had banded together before Bahamut was put into Dalamud and that Bahamut knew she was at Azys Lla. And he probably remembers Omega... So the Warring Triad and maybe Omega might be going on a rampage all over Aldenard. Meanwhile, Xande would probably be trying to open up the Voidgate for the Cloud of Darkness to come in... and Nidhogg is still assaulting Ishgard. I don't see Aldenard as we know it surviving any of that which means the Ascians would have to do their usual "wait for Society to become stable enough they start warring" thing.

The other possible explanation is that the 7th Umbral Calamity is the Calamity that marks the majority of the Shards being rejoined to Hydaelyn. That might cause Zodiark's seal to reach a tipping point where no matter what happens, it will fail. More Calamities just means it happens sooner rather then later. So some of the Ascians might decide that they should accelerate their usual time table no matter what the situation is on the Source.