I find Estinien in the Post-Endwalker patches to be so fascinating, because out of everyone, he is probably the most vocally hopeful and optimistic. That isn't to say that Y'shtola, Vrtra, Zero, and the WoL aren't, but it's Estinien who is constantly reassuring Vrtra-- We will find Azdaja, she is alive, we will find her, and we will bring her back. It's Estinien who suggest to Zero that they-- the "no longer Scions" -- will not stop until they find a way to save the Thirteenth. At every turn, at every misstep, at every roadblock, Estinien stays hopeful and optimistic.
And while some may find it out of character, I actually think it is very much in character for him, and I also think it is the natural endpoint of his character growth post-Dragonsong. Because I think that the moment that Alphinaud and the WoL ripped Nidhogg's eyes from his armor, Estinien became hopeful and optimistic. I just don't think he understood that, and I think the feelings were foreign to him, but he definitely felt them.
Because in spite of his speech to the Scions about how he views the world differently from them, in spite of him saying that he views it as a "realist" whereas they are the dreamers, the optimists, he says to Fordola earlier on "dreams worth fighting for don't die so easily." In the DRG 70 quests, he has hope that Orn Khai, himself, and the WoL will be able to aid Faunehm. Estinien Post-Dragonsong thru Endwalker is hopeful and optimistic, he just isn't ready to admit it yet.
What helps him accept it, what helps him be more openly hopeful and optimistic, is his sacrifice at Ultima Thule. I haven't read the dialogue since playing it for the first time, but based off of my own recollections, I recall him mentioning knowing that he needed to step forward and confront the dragon who was wallowing in regret and remorse. He needed to step forward, and take a risk, and that feeling he felt was I think the moment Estinien became an optimist. Because he knew, instinctively, that by doing so he would be risking his own life, but he would also be paving the way forward for the rest of the Scions.
He had no way of knowing that! No confirmation, nor proof! But in that moment, he had faith, and he had hope, and he had optimism, that in sacrificing himself the others would be able to press forward.
And for Estinien Varlineau-- the pessimist, the realist-- that was enough for him.
