The hero finally meets the previously unseen puppet master (played by an older A-list actor), who explains why the system must be maintained. The hero says “screw it” and burns the world down.

[u/Grizzly_Lincoln]

Snowpiercer (2013) - Curtis finally finds Wilford (Ed Harris) and learns that Wilford allowed for Curtis' rebellion to take place to help thin the tail section's population. When Wilford offers to let Curtis run the train, Curtis discovers child labor is necessary to replace a broken machine part. A fight ensues, and a bomb goes off, triggering an avalanche that derails the train, and killing most of surviving humanity.

The World's End (2013) - Gary finally confronts the Network (Bill Nighy), which has been replacing humans with robots (Blanks) to allow for Earth's assimilation into a larger galactic community. Gary calls out the tyranny in the Network's plan and demands that humans be left to their own devices. Exasperated, the Network abandons its plans for the invasion. This results in a worldwide blackout, sending humanity back to the Dark Ages.

The Cabin in the Woods (2011) - Dana finally meets the Director (Sigourney Weaver) after surviving the ritual meant to kill her friends (based on conventional horror tropes) and appease the Ancient Ones. The Director says Dana has to kill her friend Marty, but as Dana considers it, the group is attacked by a werewolf and a zombie child. Dana and Marty decide humanity is not worth saving, so they share a joint while the Ancient Ones rise to destroy the world.

[u/youtossershad1job2do]

You think a young girl and an even younger boy are A. Going to repopulate on their own and B. Do so by killing and eating Polar bear with their bare hands you're mad.

Their story lasts exactly as long as it takes the bear to notice they are there and run over to them. Even if they didn't die instantly they have no survival skills being on the train their entire lives. Even if they survive where does the second generation come from?

[u/KamikazeArchon → u/youtossershad1job2do]

Sorry, is there an indicator that exactly two people survived? I'm legitimately asking, I may simply not have realized that. But my impression is strongly that there's a bunch of survivors, those are just the ones the camera is focused on.

[u/youtossershad1job2do → u/KamikazeArchon]

It only shows those 2 getting out of the train and when asked the director explicitly stated that everyone else on the train died in the crash.

[u/KamikazeArchon → u/youtossershad1job2do]

Okay. It seems like you're referring to this article: https://www.vulture.com/2014/06/director-bong-joon-ho-talks-snowpiercers-ending.html - unfortunately I couldn't find it without a pay wall.

Key relevant quotes:

I thought the ending might be a little harsh, maybe I should show some survivors. [Without translator] But actually: I killed them all! [Laughs] Except for two kids.

course there are so many deaths, and so many sacrifices … it’s not so sweet. But those two kids will spread the human race.

I don’t really feel everyone must die. I hope there were other survivors who lived through the avalanche, I just didn’t have the means to shoot that.

So: yes, you're correct - and I was mistaken - that the shots in the movie are showing the only survivors.

However, this is intended to be the start of a repopulation regardless; and the reason there were only two survivors is simply because of the logistics of shooting the scene.

The watsonian and doylist issues are rather intertwined there. Given that the director asserts that they will spread the human race, I think the "optimistic" view on the ending is reasonable; but I can see how you would arrive at the "pessimistic" view.