As someone who generally enjoys darker and more morally grey stories, it isn't so much the lack of a happy ending for the Ancients that bothered me so much as the sheer lack of nuance and blame directed at the character responsible for their downfall and destruction. In a game that ordinarily handles heavy topics with a bit more tact, it simply feels incredibly out of place for Venat to be presented in the way that Endwalker portrayed.
I'm primarily a Garlean fan first and foremost. Before Endwalker, I was very wary of the way in which the destruction of their homeland would be handled. I expected smug arrogance from the Scions and dodgy implications that the Garleans had it coming. I was, thankfully, pleasantly surprised.
The Garleans weren't taken advantage of. They weren't excused for everything that they did, though it was recognised that their plight was so dire that trying to push for 'reparations' was in no way acceptable. Even after initial offers of aid were ignored, the Garleans weren't given up on. Finally - and perhaps most importantly - the story didn't ignore the weight of the Garleans having a point on some level. In the end, they were at a major disadvantage due to their typical inability to manipulate aether and had been persecuted and subjected to near genocide by forcing them to flee to the frozen wastes...where they were still being attacked until given a helping hand from Emet-Selch. That led to a reversal in their fortunes for a while though as we know it was part of a scheme to usher in the Rejoinings.
All in all, it's a pretty complicated situation that was handled with nuance. I hope it continues into the coming content patches and expansions - since at this point, the Garleans are the main element of the story that interest me.
So I have to admit, I was very baffled by the stark contrast between how the Garleans were handled compared to the Ancients. Personally if it wasn't for the Garlean conclusion being better than the Ancient's finale then I would have very likely quit. The only reason I'm giving 6.1 a fair chance is because there is a good story at times mixed in with the rest of Endwalker.