Varis' claim to the throne was stronger than Titus' due to Varis having an heir in the form of Zenos. Titus' forces launched an assassination attempt on Zenos - which failed - as confirmed in Yotsuyu's short story. So if Titus was willing to resort to assassination it doesn't seem like he was the perfect figure some suspected he would be. Furthermore, even if he had succeeded and managed to take out Varis as well...he would have found himself in the same position as Varis. Namely at the mercy of at least two powerful Ascians.

It's also not the Populares that are the first group of Garleans loyal to their homeland to work alongside the Warrior of Light and put it on the 'right track' - Regula van Hydrus and the remnants of his forces are the first. It was a brief, temporary alliance but a promising one nonetheless. Especially given Regula's close relationship with the Emperor.

I'd also point out that the Populares and Optimates are based on real world factions...and neither of them were exactly pure and virtuous. They desired control and power above all else, at times refusing to compromise with the other.

The Eorzean Alliance's recent imperialistic tendencies on the world stage are also going to be a problem moving forward. After all, Eorzea has already shown a willingness to sabotage Hingashi by trying to get around Kugane's trade tariffs. In short, it is more than willing to engage in trade wars. Given that Hingashi has suffered its own troubles in the form of strife and conflict, it's a case of outright cruelty on Eorzea's part.