I could see the toll it might take on him to know he was aging, know he was getting ill easier and more often, to ramp up that last great effort to secure his legacy, only for it to not only fail to purge Eorzea of eikons, but free an imprisoned eikon, revealed to have long-ago tempered the very (wo)man he put in charge.
The added characterization of the factions and leaders in Garlemald could also go a long way towards handwaving some of the inconsistencies in Gaius's reputation and behavior if the war of succession already being clandestinely waged.
Baelsar was pro-conquest, but anti-Garlean supremacy in the way that most purebloods behave. Titus, backed by the Populares, would grind the wheels of conquest to a halt, forsaking Garlemald's solemn duty as rulers of might to lead and deliver the world from the blight of eikon and shadow. Those who opposed the Populares, especially the Optimates, would be driven to rally behind Varis, whose victory would ensure that not only those who opposed order and Garlean rule would be stamped out, but that the whole of Eorzea would be ground under the heel of a "superior race" that had no love for them; the death of meritocracy. (Ignoring that he'd have be replaced with Regula ten minutes later, anyway.) From his point of view, if Eorzea was to be conquered right and ruled well, it had to be him, and it had to be then.
That adjusts a lot of context into a more comfortable place.
(Ironically, it could have helped clean his arc up even without bringing him back ... but I'm still happy to see him.)
Moreover, with regard to the Tale, it's really nice to see some of the finer points of the in-game dialogue laid out conclusively. It often fell by the wayside to a degree that Yotsuyu displacing her desire to kill her adoptive family onto all of Doma was a very specific kind of [They're complicit because they let it happen.] whereby the very core of Doman culture encouraged sweeping abuse (and the abused along with it) under the rug. Her avenue for forcing Doma to confront that injustice was a deplorable sort of vengeance, but she never pretended it wasn't.