How are the Scions succumbing to their own hubris? At least, any more so then they usually do. Everything since 2.0 started (for that matter, 1.0) has been based on the Scions working with whatever information they have available to them at the time. And so far it's worked out pretty well for them. They have very little reason to stop doing what they do.

I think the only time they've "succumbed to their own hubris" as you put it was when Alphinaud created the Crystal Braves. And he's determined since then to not do that again.

Like it or not, the Scions are considered experts in their respective fields by an organization that is arguably the most well educated organization known to the three continents. They are Archons for a reason. If they don't decided to do certain things, no one else in Eorzea is going to because everyone knows the Scions have spent way more time studying esoteric subjects then they have. Anyone else who might have a better understanding of things is back in Sharlayan and doesn't want to insert themselves into making history. Which the game has said time and time again isn't right. The last thing FFXIV has ever treated as a good thing is passivity. I highly doubt it's going to start treating it as a good thing now.

And while the Warrior of Light is powerful, it's highly implied that previous Warriors of Light were even more powerful then they were... And even they couldn't prevent a Calamity! We've seen a good amount of evidence that the overall power of the Warriors of Light has decreased over the eras instead of increased. If anything, I keep thinking the WoL and the Scions will have be doing more rather then less to make up for the power loss over the eras.