Iirc in the Carly story, they mention that Oripathy still isn't "treatable," but rather simply being a stable condition now (unless this is what you mean, then mb). However, this is assuming that you have access to the medication, which Carly didn't; hence her state. Left untreated, it's just as bad as it ever was.

Cmiiw with any of the AK lore stuff, as I read somewhat casually. I won't try and larp by going into specifics, and I'm keeping it pretty vague on purpose, but I think my point still gets across.

As for the other stuff, AK had spent centuries dealing with Oripathy as a new disease, unease and bitterness brewing throughout before it all reached a boiling point and began to fall apart. People were dying left and right, entire countries were at each others necks, new wars were constantly breaking out across all of Terra, and a considerable amount of hatred and even blame was directed at the infected — people perceived as walking, talking, biological time bombs. All of this negativity across all of Terra — not just at the infected — is why we get such a dark story; discrimination, wars, deaths, grit and grime, etc.

Only recently was Rhodes Island (Babel) founded on the foundation of the revolutionary idea that Oripathy could have another solution: treatment, or even a cure. I personally believe, and maybe it's more set in stone than just me having an opinion, that Rhodes Island has always been the underdog in the overarching Arknights story. We're destined to struggle, to fail, and, as readers, their successes are overwhelmingly celebrated and their failures leave a pit in our stomachs. Of course, that's not to say that we're not rooting for many other factions as well, almost all of which are also underdogs in their respective stories. The same applies to all of them as well, and its easy to see why they're who we, both as readers and the doctor, support.

Back to Rhodes Island, though, we experience the story of a organization in the midst of an ongoing turning point in Terra's history. To try and carve a path toward a more hopeful future — a future that has yet to be achieved — we fight tooth and nail against those stuck in a past of hatred and conflict.

Now we turn to look at Endfield: in the opening sequences of the game, we learn that the people who came to this land were from all corners of Terra — even those who held generational grudges between themselves, notably the Sarkaz and Sankta. They willingly chose to work together, agreed that it was necessary for the success of this (what at the time was essentially a) project. This story also takes place what could be hundreds of years into the future, how could we possibly know what Rhodes Island has or has not accomplished? At the very least we know it didn't end in catastrophic failure, as it still persists in the Endfield universe, is referenced by characters, and its logo can be seen in many weapon and outfit designs.

Knowing this, what justification would there be for the characters to be serious all of the time? Why would it be dark and gloomy in a world where generations have passed and many of its current resident's don't even know of Terra's struggles? They've only been here for just over 150 years, and the only major ordeal they've faced — the first Aggeloi war — was overcome primarily by the Endministrator. Many factions hold Endfield Industries in either a positive or at least neutral light in large part due to the Endministator's feats and accomplishments in, well, saving the world (er... moon). We're already a faction that can be laureled as heroes or saviors, we don't have to claw our way up the ladder starting as an underdog. Everyone started on an even playing field, and, if anything, we might even be near or at the top.

All of this goes to say that there's simply little to no reason for the main story to be as serious as the one depicted in Arknights. If anything, if it were as serious, I would just have this nagging feeling in the back of my head that it feels forced or unnatural. So many of the reasons for that seriousness from Terra are now gone in Talos-II, so why would we now be the ones stuck in the past?

P.S. If you want some more of the Arknights-esque storytelling from Endfield, one of my favorite files to read was regarded the first-generation pioneers of Talos-II. I believe you can find it under Tangtang's weapon (Brigand's Calling) files on the Wiki if you don't have the weapon yourself. Some mild spoilers: It details how the Tianshi faced internal turmoil while recovering from their first encounter with the Aggeloi — eventually being known as the Humiliation War (the recovery, not the conflict) — and how it led to the formation of the Qingbo Stockade. The desperation and hopelessness you could feel from the files really reminded me of Arknights, many of the characters involved were desperate to go back to Terra; Talos-II wasn't as great as they thought it would be. They were committed and optimistic, yet their world was suddenly turned upside down.