I can understand why some don't like the ending, but I honestly don't see what they could have possibly given us that would actually feel satisfying and be as dramatically effective. Besides, to me, the terrifying uncertainty of it all kind of *is* the point. There is no closure, no satisfying payback. There are no winners. There can't be.
Of course it's hard to disentangle the viewing experience from contemporary world politics, and the subject matter hits particularly hard given the state of affairs today. I had the same reaction as you - these people are mostly acting pretty reasonably given the circumstances, and even then it's an impossible and terrifying situation. Then you start thinking about how this would have played out under the current leadership in real life. In fact, I've been worrying about that quite a lot for some time now. It's... concerning.
Feels like we're back in the Cold War again - except this time it's multipolar, everyone is stupid, and all the adults have left the room.
As a minor side rant: I've long been ambivalent about much of Bigelow's output. Particularly her most famous work. Hurt Locker felt to me like it was trapped in the Uncanny Valley of Seriousness: trying hard to be a gritty realistic military drama, but ruining it by having no shortage of unrealistic nonsense in the plot and character behavior (as the vets have written about at length). Zero Dark Thirty was pretty good as a movie, but did leave a bitter aftertaste because it felt like it was trying to whitewash the legacy of the Enhanced Interrogation affair as being crucially important to the investigation and probably not all that bad. Which I think is both historically and ethically questionable. But both are quite cinematically good and stylish, I suppose, so no questioning her abilities there.
Thus far my favorite is actually her golden oldie, the original Point Break - ridiculous 90s action blockbuster schlock in all its glory, starring none other than Keanu "Whoa" Reeves. Not exactly high art, but it's pretty fun! I believe James Cameron was involved in the script as well. Kinda makes sense. I always thought it felt vaguely similar in style and feel to his own work around that time.
Ah well... I guess I need to see Threads next to complete the circle, eh?